Iseult is a useful, award-winning tool with numerous prizes, that lets you optimize your photos so they are easier to send via email to friends and family, upload to a blog or to a webpage.
For this, Iseult resizes them to convert them into thumbnails. You can resize thousands of images at once (this trial version only lets you convert 35 at once), working with the following graphic formats: BMP, CUR, FlashPix, GIF, ICO, JPEG, PCX, PICT, PNG, Portable Anymap (PBM / PGM / PPM), PSD, Sun Raster, TGA, TIFF, WBMP, XBM and XPM.
It has its own image viewer that includes three modes of working: thumbnail, thumbnail with fixed size, and zoom. The processed images are saved in JPG format (without losing quality).
For it to work correctly you need to previously install Java Runtime Environment.