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Caesium Image Compressor vs Klia Kompress: catalog facts
Caesium Image Compressor	Klia Kompress
Free Free and open source under the GPL.	Free No price is mentioned; the app is published on Flathub under a proprietary EULA.
Windows, macOS, Web	Linux
Batch processing with visible before and after sizes for the whole folder Resize at the same time as compressing, in one pass	Processes files locally without uploading Batch conversion with quality control
No official Linux binary; you compile it or use a third-party build Windows 10 build 1809 or later and macOS 12 or later, 64-bit only	Proprietary, source not published Very new project with little history
Downloadable app, Web application	Downloadable app
Open source	Closed source
License: GPL-3.0	License: Proprietary EULA
No account needed	No account needed
Works offline	Works offline
Official website Full listing and sources Checked September 21, 2026	Official website Full listing and sources Checked October 1, 2026

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