Caesium is a free, open-source online tool for compressing photos and images, designed to help users save storage space and make uploads faster. The service provides a straightforward workflow: users can add images by dragging and dropping files or browsing their device, then adjust compression settings and review their results. Available controls include quality and size modes, a quality setting, lossless compression that preserves image quality, and an option to keep metadata.

Caesium supports JPG, PNG, and WebP files, with a limit of 10 images per batch and 20 MB per file. The tool also offers batch processing and image previews, making it useful for handling multiple files and checking changes before using compressed images. Caesium states that images never leave the user’s device, addressing privacy concerns when working with personal or sensitive photos.

The interface is available in several languages, including English, Spanish, French, Italian, Polish, Ukrainian, and Chinese. The service is associated with SaeraSoft and Matteo Paonessa