TinyJPG!

TinyPNG uses smart lossy compression techniques to reduce the file size of your PNG files. By selectively decreasing the number of colours in the image, fewer bytes are required to store the data. The effect is nearly invisible but it makes a very large difference in file size!

JPEGmini is a patent-pending photo recompression technology, which significantly reduces the size of photographs without affecting their perceptual quality. The technology works in the domain of baseline JPEG, resulting in files that are fully compatible with any browser, photo software or device that support the standard JPEG format.

Photo Size Optimizer for Mac:

iLoveIMG is an online service to work with images completely free and easy to use. Compress images, resize, crop, convert and much more!

Lossless Photo Squeezer for Mac is a professional image size compressor which will reduce your PNG, JPEG and GIF photos and images size with LOSSLESS quality. You can optimize all your photos to save much hard drive space, web space and share full-resolution photos online more faster.