Iseult let you make thumbnails from a large bunch of images on mac.
Edit by : You need to share your last digital photos with your friends, by sharing them over the Internet (mail, website, blog)So you want to make thumbnails from a large bunch of images. No problem, with Iseult, the work is done with just a couple of mouse-clicks.

-Deployable with Java Web Start.
-Scan your hard drive for supported images.
-Original and intuitive FTP-like interface.
-Image viewing capabilities.
-Load images in the following formats : BMP, CUR, FlashPix, GIF, ICO, JPEG, PCX, PICT, PNG, Portable Anymap (PBM / PGM / PPM), PSD, Sun Raster, TGA, TIFF, WBMP, XBM, XPM.
-Three processing modes: Thumbnails, Thumbnails with fixed size, Zoom.
-Log manager.
-Save processed images to JPEG (with control over image quality level).
-International support: english, french and spanish are fully supported (interface and documentation).
-Registered version can process thousands of images at a time, whilst an evaluation version is limited to 35 images. you can free download Iseult for Mac OS X 1.1 now.