Substack covers and post heroes that hold a publication identity

The Substack image playbook, in one preset

Substack's image specification is documented per slot in the publisher Help Center, and the slots that matter most for subscriber growth are the publication cover, the post hero, the publication icon, and the author headshot. The publication cover and post hero are both 1456×816 px (≈16:9) — Substack's documented upload size — and they render across the publication homepage header, every post card on the publication's main page, the email preview that lands in subscriber inboxes, the post page header, and the Twitter and OG cards that drive social-share top-of-funnel traffic. The publication icon is 240×240 PNG with an alpha channel; it renders in the navigation chrome, the email signature line, and the iOS / Android Substack apps, and the alpha channel matters because dark-mode rendering breaks on flat JPEGs that produce a white halo. The author headshot is 600×600 square; the podcast cover (for publications distributing audio) is 1400×1400 square to match Apple Podcasts. JPEG and PNG are both accepted; the per-image cap is 5 MB on web upload.

The design rule that drives Substack subscriber growth isn't technical — it's consistency. A publication cover, post heroes, and author headshots that share a colour palette, an illustration style, and a composition formula signal a developed creative practice that prospective subscribers can trust their email address to. Pages where each post hero is in a different style on a different background palette read as low-effort and hurt the conversion from public-page visit to subscribe. Substack's content policy is permissive but specific. Adult or sexual imagery on the cover violates the content guidelines even on suggestive-fiction newsletters; adult-fiction publications can use suggestive but not explicit cover art. Copyrighted character art and brand logos used without licence trigger DMCA takedowns, and repeated offences result in publication suspension. Watermarks are allowed and common — independent illustrators often watermark hero images for original artwork. Stock photos from Unsplash, Pexels, and Adobe Stock are common in news / opinion / explainer publications when properly licensed.

Why a cohesive image set converts more Substack subscribers

Substack's funnel is short — public page or email preview to subscribe button — and the visual identity is what carries the subscribe decision once the topic and writing voice land. Publications with a cohesive image set across the cover, every post hero, the publication icon, and the author headshot outperform publications with mixed aesthetics in the platform's own creator-success data, because the consistency reads as a sustained creative practice the subscriber is buying into for months. Cross-post previews on Twitter and other social surfaces use the same hero image, so the visual identity carries from on-Substack discovery to off-Substack social distribution — and the publications that look professional on Twitter convert better when the link clicks through. Running the publication's full image set through the preset before the next launch or refresh is the cheapest subscriber-growth lift available without changing the writing itself, and the visual coherence sustains across the months and years that matter for compounding the subscriber base.