There are to standard formats for pictures on the world wide web. They are GIF and JPG.

JPG are pictures in true color (16,7 Millions). They are heavily compressed (with data reduction) to save space.
You should never use JPG if your bitmap have big surfaces of the same color - the reduction will make some undesirable noise. See example to the left. However, you can choose low compression to minimize the problem. In Paint Shop Pro choose File, Save As, Options, JIF/JPG, DPI to be saved: 9999, Compression level: 1

• JPG pictures cannot be transparent.
• JPG pictures cannot be animated.
• JPG pictures are non-interlaced.

GIF are pictures in maximum 256 colors. They are slightly compressed without data reduction.
The compression works best with big surfaces of the same color.

• GIF pictures can be transparent.
• GIF pictures can be animated.
• GIF pictures can be interlaced or non-interlaced.