Comparing two images sounds simple until you try to show someone else the difference. A screenshot loses the interaction. A side by side crops both images small and makes the viewer’s eyes do the work. What you usually want is a slider you can drag across a before and an after, and then a link you can send.
The classic tool for that job, imgsli, has been offline for months; there’s a full write-up on the switch if that’s what brought you here. Its absence reshuffled the field, so here’s what’s actually worth knowing in 2026, grouped by the job each tool does. Every claim below was checked against the live sites in July 2026, not copied from year-old listicles.
Lightweight “make a before/after and share it” tools
The category most people mean by “image comparison tool”: upload two images, drag a divider, share the result. No install, no code.
imgi
imgi (this site, so judge the framing accordingly) turns two images into a shareable before/after slider. Drop them in, drag horizontally or vertically, publish, and you get a permanent short link. What separates it in this group: every comparison also has a one-line iframe embed for your own site, an export to GIF, MP4, or WebP for places that won’t host a live slider, and room for up to ten images in one comparison with a dropdown to switch pairs. Related comparisons can be grouped into albums under a single link. Served images are your exact uploaded bytes, never re-encoded, which matters when the fine detail is the whole argument. There’s an offline mode that runs entirely in your browser, and no signup to start. Pro at $3.99/mo removes the export watermark, adds private uploads and ad-free viewer pages, and raises animation limits.
Best for: showing a difference and sharing it anywhere, especially for modders, upscalers, photographers, and designers.
Try it, this one’s live:
imgdiff.net
A clean browser tool with a drag divider plus zoom, pan, and fullscreen. Two images, editable Before and After labels, and a public share link; there’s an offline mode too. Anonymous uploads are public with no password, and the site itself warns against uploading sensitive files, credit where due for saying it plainly. A free account adds a small dashboard with saved sessions and favorites.
Best for: a quick, no-frills two-image comparison with a share link.
pxcmp.com
Bills itself as a pixel-perfect 4K comparison tool for gamers and developers, and the spec list backs it up: BMP, PNG, JPEG, and WebP, up to twenty images at 32 MB each, zero re-compression, RAW support, files stored for a year. You can also skip uploading entirely and import up to twenty images by pasting direct URLs. The quirk: direct uploads need a free access key you request from the maintainer via Reddit or email. It runs no ads and no trackers on a personal server, which is charming and also the thing to weigh when you decide where your comparisons should live long-term.
Best for: lossless, high-resolution comparisons where quality and image count matter more than instant access.
Heavyweight diff and QA tools
Built to measure differences rather than present them. Different job, different audience.
Diffchecker
The big one. Its image mode has side-by-side, highlight, fade, and slider views, takes JPG, PNG, WebP, GIF, HEIC, and PDF, and layers on auto-alignment, change detection, OCR for text inside images, and EXIF metadata comparison. It also diffs text, Word and PDF documents, Excel, and folders, which tells you who it’s really for. The free web tier is generous on core views but caps extras (PNG export is five per month); paid runs $15/user/month for Pro plus the desktop app, $20 for Legal, $40 for Enterprise.
Best for: QA engineers, lawyers, and document reviewers who need to catch and prove changes, not show off a retouch.
slow.pics
Running since autumn 2017 and beloved by the video encoding community. You upload sets of frames and flip between them with clicks or keyboard hotkeys, and it hands you thumbnails plus HTML and BBCode links for forums. It treats quality seriously in a specific way: BMP and TIFF uploads are losslessly converted to PNG, and PNGs are losslessly recompressed. Worth knowing: images unviewed for two years may be removed, so it’s a working surface more than an archive.
Best for: encoders comparing frames across settings or codecs, and anyone living in BBCode forums.
Developer libraries, if you’d rather build it
For a slider inside your own product, write a little code and host the images yourself. JuxtaposeJS from Northwestern’s Knight Lab is the veteran: free, open source, embeds via iframe, but you supply image URLs (their docs suggest Flickr, Dropbox, or Google Drive if you don’t run a server). img-comparison-slider ships React, Vue, and Angular wrappers. TwentyTwenty is the old jQuery standby. Full control, zero convenience: no hosted share link, no gallery, you own every pixel of the plumbing. The embed guide covers the paste-one-line alternative if the plumbing isn’t the fun part for you.
How to pick
- Show a difference and share it fast: a lightweight tool. imgi if you want an embed, animated export, or many images; imgdiff.net for a bare-bones two-image share; pxcmp.com when lossless 4K is the point and requesting an access key doesn’t bother you.
- Measure and prove a change, for legal, QA, or document review: Diffchecker.
- Compare encoder output frame by frame: slow.pics.
- Building your own product: a library, and budget time for image hosting.
One category deliberately missing: single-purpose “photo diff” apps that appear, collect a domain’s worth of SEO traffic, and vanish. The tools above have either a business model, an institution, or years of track record behind them, which is the quiet thing to check before you paste any comparison link into work that outlives the week.
For most people replacing imgsli, the lightweight category is the answer, and the drag-publish-paste flow takes about ten seconds to try.