Images

JPG

• 24-bit color, grayscale; lossy compression; interlacing
• Well suited for photos

PNG

• Portable Network Graphics
• Multiple color depths; lossless compression; interlacing; palette-based and alpha transparency; gamma correction; text annotations; a subset of mng
• Pronounced "ping"

Transparency

• No support: IE <= 6 (inadequate support), NS4

Alpha transparency

• 24-bit color, 8-bit alpha channel (32-bit total)
• Support: FF, IE7+, Safari, Chrome, Opera 6+, Moz, NS6

Binary transparency

• 8-bit color (presumably, using a 256-color index, with one color representing 100% transparency)
• Support: FF, IE6+, Safari, Chrome, Opera

GIF

• 8-bit color; lossless compression; proprietary format; palette-based transparency; interlacing; animation
• Well suited for icons, diagrams, and user-interface elements
• Pronounced "jif"

SVG

• Scalable Vector Graphics
• Supports audio, video, and animation

MNG

• Multiple-image Network Graphics
• Animation of PNG and JPG images; supports transparent JPGs
• Pronounced "ming"

• Only supported by Konqueror

JNG

• JPEG Network Graphics
• Combines jpeg with alpha transparency; a subset of mng

Misc

• Interlaced GIFs are equivalent to progressive JPGs.