Why You Need a Tool At All
Google Photos has no built-in way to find duplicates already in your library. It blocks re-uploading an identical file, but anything resized, cropped, re-compressed, or re-saved counts as a new file. So a free third-party finder is the only realistic option short of scrolling through everything by hand.
The catch with 'free': most tools let you scan and preview for free, then charge to actually delete in bulk, or cap the free scan at a small number of photos. Below is what each option really gives you before any paywall.
AiCleanerPro Cloud — Free in Early Access
AiCleanerPro Cloud connects to Google Photos and Google Drive via read-only OAuth, scans thumbnails with perceptual hashing, and groups exact and near-duplicates with the best copy marked. It is the only option here that does cross-service detection (the same photo sitting in both Photos and Drive) in a single scan.
It is free for the first 1,000 early-access users with full feature access — no item cap, no card required. Full-resolution photos are never downloaded; everything runs in your browser. Join at google.aicleanerpro.app.
Google Photos Duplicate Remover (Chrome / Edge Extension)
This browser extension scans your Google Photos library in place and groups identical and similar photos and videos. It is the most established free option and the one most listicles point to.
The free tier analyzes up to 100 photos or videos per scan, which is fine for a quick pass but tedious for a large library. It works on Photos only — it does not look at Google Drive. Privacy-wise it runs locally in the browser.
AiCleanerPro Cloud
Find duplicates, blurry photos, and similar shots across your entire Google Photos and Drive library. Browser-only, thumbnail access, 100% private.
Join Free Early Access →gpdrm.com and Cloud Duplicate Finder
gpdrm.com (Google Photos Duplicate Remover, web version) is a browser-based freemium tool that finds duplicates in Google Photos without an install. Detection is solid for exact copies and weaker on near-duplicates.
Cloud Duplicate Finder scans Google Drive (plus Dropbox, OneDrive, and Box). The scan and preview are free, but deleting requires a premium subscription. It is a better fit if your duplicates are mostly in Drive rather than Photos.
Open-Source: google-photos-deduper
If you are comfortable with developer tools, mtalcott's google-photos-deduper is a free, open-source Chrome extension on GitHub that finds and removes duplicates from Google Photos. It has no item cap and no paywall, but it needs more setup than a one-click tool and has no cross-service support.
For most people the friction outweighs the savings. For a developer who wants full control and no account limits, it is the most genuinely free option.