Info: Web Designer’s Guide to PNG Image Format

http://sixrevisions.com/web_design/web-designers-guide-to-png-image-format/#more-4429

When to Use Each Format

Here is a simplistic summary of the file format comparisons:

• Use PNG-8 over GIF for images with simple colors (logos, icons, buttons)
• Use PNG-8 over JPEG for images with simple colors (logos, icons, buttons)
• Use PNG-24 over GIF for photographic images
• Use PNG over JPEG when using alpha transparency
• Use JPEG over PNG for photographic images
• Use GIF for background transparency for older browsers (IE6 and below)
• Use GIF for animated GIFs