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gThumb vs FastStone Image Viewer: catalog facts
gThumb	FastStone Image Viewer
Free Free and open source under the GPL version 2 or later.	Free Free for personal use. Commercial use requires a paid licence, and the related FastStone…
Linux	Windows
Native GNOME desktop application Works on local folders without a server	Handles every common format including HEIC, WebP, PSD, PDF and camera raw Browser, viewer, basic editor and batch converter in one small program
Linux only No cloud sync or phone backup	Free for personal use only; commercial use requires a licence Windows only
Downloadable app	Downloadable app
Open source	Closed source
License: GPL-2.0-or-later	License not stated
No account needed	No account needed
Works offline	Works offline
Official website Full listing and sources Checked September 23, 2026	Official website Full listing and sources Checked September 21, 2026

Catalog facts only. Anything “not stated” is unconfirmed. Check full listings for details.