Magic Eraser + Substack: Newsletter Hero Photos, Notes, and Email Inline Imagery

No native plugin — Magic Eraser is a web/iOS/Android image editor that runs outside the Substack post editor. The workflow is: prep images in Magic Eraser, export at full resolution (PNG or JPEG), then upload to Substack through the standard image-upload flow in the editor. Substack's image pipeline handles the WebP conversion, responsive srcset, and CDN distribution from there. For most writers, the lack of a direct plugin isn't a friction — image prep happens in batches at a different point in the workflow than post writing, and the separation actually helps with consistency (one editing session per week's image batch, then per-post uploads as posts ship).

Substack recommends 1456×816 as the source for the post hero image, which gives the platform enough resolution for the post-page full-bleed render and the responsive downsampling to recommendation-feed thumbnails, email-delivery render, and 1200×630 OG share card. Magic Eraser's AI Fill outpaint solves the common composition problem of phone-camera source photos that aren't natively 16:9 — start with whatever source you have, AI Fill out to 1456×816 with margin to spare, and Substack's responsive pipeline handles the downsampling across every render context cleanly.

No. Upload the highest-quality source — Substack's image pipeline serves automatic WebP, builds responsive srcset for every breakpoint, and applies its own compression based on viewport and connection. Pre-compressing images before upload (saving as 80% JPEG, for instance) just compounds with Substack's own compression and produces visibly worse output at every render size. Magic Eraser exports at full quality by default — keep that quality through the upload step and let Substack handle downstream optimization.

Define the publication's visual recipe upfront and save it as a Magic Eraser preset: one AI Filter color-grade preset for the photographic-look identity, one Background Eraser brand-color palette, one composition discipline for hero photos (subject-centered, subject-left, subject-right based on the publication's editorial voice). Apply the same recipe to every post hero, every Notes image, every email-inline image. Over months and years, the cumulative recipe discipline produces an archive that reads as one coherent body of work — which signals editorial seriousness to new subscribers browsing the archive and reinforces returning-subscriber recognition.

Yes. Substack Podcast cover art uses the same 3000×3000 square dimension as Apple Podcasts and Spotify (covered in detail by the podcaster-cover-art-ai-workflow blog post on the same site). The cover renders at 3000×3000 on the podcast landing page, at smaller sizes in the Substack home feed and podcast directory, and at thumbnail size in directory-list contexts. Magic Eraser's cover-prep workflow: AI Fill outpaints the source photo to 3000×3000 square, Background Eraser applies the publication's brand color, AI Enhance sharpens for crisp render at thumbnail size, and title typography at 80-100pt proportional carries the show title. Run the 100×100 thumbnail test before publishing — Substack Podcast renders at thumbnail size in feed where the cover competes for attention against other podcasts and other Substack content.

Substack's built-in image editor handles upload, cropping, and basic positioning — useful for in-the-moment adjustments inside the post editor. Magic Eraser handles operations Substack's editor doesn't: object removal (distractions, unintended people in the frame, watermarks from stock-photo sources), background swap (cluttered home backgrounds to clean brand-color), AI Fill outpainting (extending source photos to the 1456×816 hero aspect or 1080×1080 Notes aspect), and AI Enhance (upscaling and sharpening low-light phone photos to retina-display resolution). The right shape is sequential: prep in Magic Eraser first for the major transforms, then use Substack's editor for the final upload and positioning.

Inline images in Substack email deliveries render at 600px wide across the most-common email clients (Gmail, Apple Mail, Outlook, Yahoo Mail), regardless of subscriber device. The constraint to design for: subject visibility at 600px render, retina-display sharpness for users on iPhone / iPad / high-DPI desktop screens (which means uploading 1200×600 source for 600px display), high-contrast composition that doesn't rely on subtle gradients (some email clients render gradients poorly), and conservative file sizing (Gmail clips emails larger than 102KB total, so individual images should be 80-150KB max). Magic Eraser's full-quality export combined with Substack's downstream optimization typically produces inline images in the 100-200KB range — within the Gmail clip threshold and supporting retina render across modern email clients.