AI Images for Email Marketing: What to Generate, What to Leave Out, and the Sizes That Do Not Break
Email is the one marketing channel where a beautiful generated image can fail without anyone noticing. The client blocks it, and the reader sees a grey box with your headline inside it, invisible. Dark mode inverts the off-white background into charcoal and your illustration floats in a void. The file is 900 KB and the email loads in pieces. The image-to-text ratio tips a filter. None of that shows up in the preview you approved.
So this is a practical guide to AI images in email, written from the constraints backward. What to generate, what to leave out, the sizes and weights that survive the clients, and a table by email type. It assumes you already know how to make an on-brand image; if not, Turning Brand Guidelines into an AI Image Brief comes first.
The four ways email breaks images
Blocking. Outlook desktop blocks external images by default, corporate webmail commonly does, and a share of readers on every client have images off. Gmail and Apple Mail display images by default through proxies, which is why the share of readers who never see your image is smaller than it was a decade ago and still far from zero. Design assumption: a meaningful number of recipients see the email with every image replaced by alt text.
Dark mode. Clients that support dark mode may invert or partially recolor your email. A light illustration on a white background can end up on near-black; transparent PNGs can lose their edges; text rendered inside an image does not adapt at all. Test in at least one dark-mode client before every send.
Weight. Heavy images slow the open and, on some clients, get clipped or lazy-loaded. Generators output large files by default; a 2K PNG hero is often over a megabyte. Compress every image before it ships.
Ratio. Image-heavy, text-light emails are a classic spam-filter signal and an accessibility failure. One hero and perhaps one supporting image, with real text carrying the message, keeps the ratio honest.
Every rule below follows from those four.
What to generate
One hero. A single image at the top, under the headline or beside it, that sets the scene for the email’s one idea. Research summarized by email tools consistently lands on one to three images per marketing email, with one hero and at most one or two supporting images. For most sends, one is right.
Possibly one supporting image. A product screenshot, a real photo, or a second illustration that earns its place by explaining something the text cannot. If you cannot say what it explains, cut it.
Nothing else. No decorative dividers, no generated icons per section, no background images (unsupported in several clients). Emails with more images look busier and perform worse.
What to leave out
Text in the image. Ever. When images are blocked, a headline inside the hero does not exist. Screen readers cannot read it. You cannot A/B test it, translate it, or fix a typo without regenerating. And it pushes the image-to-text ratio the wrong way. The subject line, preheader, headline, body, and call to action are live text; the image is a scene. Text in AI Images After GPT Image 2.5 makes the full case; email is the channel where it is not even a judgment call.
Photoreal stand-ins for real things. A generated “customer,” a generated “support team,” a generated office. If the email is about a real thing, use the real photo. If you do not have one, illustrate the idea instead. The trust guide explains why the discovered fake costs more than the missing photo.
Fine detail. Full-width heroes display at about 320 pixels wide on phones. Small elements, thin lines, and intricate scenes turn to mush. Generate for the phone: one clear subject, generous negative space, high contrast.
Your logo, drawn by the model. Composite it after, or leave it in the email header where it already is. How to Put Your Logo on AI-Generated Images covers placement.
The blocked-image test. Before approving any email, view it with images off. If the message still makes sense, the headline is readable, and the call to action is clickable, the image is a bonus. If the email is a grey box with a button, the image was doing a job that text should do.
The sizes and weights that survive
| Spec | Value | Why |
|---|---|---|
| Design width | 1200 px for a 600 px display column | 2x for high-density screens; most templates are 600 to 640 px wide |
| Hero aspect ratio | 2:1 to 3:2 | Tall heroes push the message below the fold on mobile |
| Mobile check | Legible at 320 px wide | Full-width on phones |
| File weight | Under ~200 KB per image after compression; under ~1 MB total | Load time; clipping on some clients |
| Format | JPEG for photographic; PNG for flat illustration; avoid transparency | Transparent PNGs misbehave in dark mode |
| Alt text | Every image, descriptive, under ~125 characters | Blocked images and screen readers |
| Background images | Avoid | Unsupported in several major clients |
| Animated GIF | Only if the first frame stands alone | Some clients show only frame one |
Generators do not output email-ready files. Plan for a resize and compress step, or use a tool that does it when the image lands in the email.
Illustrated or photo, by email type
| Email type | Default imagery | Notes |
|---|---|---|
| Product or feature announcement | Real screenshot or product photo, or an illustrated concept of the benefit | Feature announcement emails are about a real thing; show it |
| Newsletter | Illustrated, one style, every issue | Consistency across issues is the whole brand value; references on every generation |
| Nurture sequence | Illustrated concept per email, same style throughout | The sequence should look like one author; onboarding sequences especially |
| Promotional / seasonal offer | Styled photoreal or illustrated seasonal scene | Clearly styled, never documentary; no text in the image, the offer is live text |
| Event invitation | Illustrated “save the date” before; real photos after | Never a generated crowd |
| Win-back / reactivation | Illustrated, warm, simple | Win-back sequences are read by people who left; keep it honest and light |
| Customer story / testimonial | Real photo of the real customer, or no image | Never a generated person |
| Transactional | Usually none | Speed and clarity; a logo header at most |
Two patterns hold across the table. Illustrated wins for anything abstract or serial, because it carries no photoreal tells and holds a style across a sequence. Real wins for anything real. Photoreal generation gets one job: clearly styled scenes that do not claim to be documentary.
The workflow that makes it easy
Most email image problems trace to sequence: the image was made first, in a chat window, before the copy existed, so the headline got typed into the prompt and the image got sized for nothing in particular. Reverse it.
- Write the email: subject line, preheader, headline, body, call to action. All live text.
- Generate the hero for that email, with the prompt describing a scene that supports the one idea, in the brand’s illustrated style for this channel, with references attached, no text, one clear subject, room to breathe on a phone.
- Resize to 1200 wide, compress, write alt text that describes the scene in one sentence.
- View with images off. View in dark mode. Approve.
That order is how Marqeable’s email builder works: the copy is written and checked first, the hero is generated inside the email draft with the copy already known, from your brand profile and reference board, sized and placed in the template, with the headline staying as text and the logo already in the header. The draft waits for approval before anything sends, and the same image can be reused for the matching social post without a download. We are in private beta with a small early cohort: get early access if you would like the four steps to be one.
Frequently asked questions
How many images should a marketing email have?
One hero, optionally one supporting image. More than three is where load time, spam signals, and attention all start to suffer.
Can I generate a different hero for every email in a nurture sequence?
Yes, and you should, as long as they share one style. Generate them from the same brand profile and references so the sequence reads as one author, and vary the scene, not the style.
What about GIFs and animated heroes?
Fine if the first frame works alone, since some clients show only that. Keep them small. Generated video is a different subject and heavier than most emails can carry.
Do AI images affect deliverability?
Not as AI images. Heavy files and image-heavy, text-light layouts affect deliverability regardless of how the image was made. Follow the weights and ratio above and the source of the image is irrelevant to the filter.
The bottom line
Email punishes images that were made without email in mind: blocked, inverted, heavy, or carrying words nobody sees. Generate one hero for the email you already wrote, in your brand’s style, with no text and one clear subject, at 1200 wide and under 200 KB, with alt text, checked with images off and in dark mode. Illustrate the abstract, photograph the real, style the seasonal. Then the image is doing the only job an email image can do, which is to make a message that already works land a little better.
Marqeable runs your campaigns, answers every visitor, text, and email in seconds, and turns them into booked jobs and meetings - even at 9pm on a Saturday. We’re in private beta with a small early cohort. Get early access
