Generally people will stick to .GIF (Compuserve Graphic Interchange Format) or .JPG (Jasc JPG Compression).
This file format is restricted to 256 colours and is normally used for line art, small graphics and buttons. Because of it's linear format file sizes can easily become unmanagebale if you try and save complex pictures as a .GIF.
This format can also allow a transparent colour or background.
This is a compressed image format that works well for photos, complex images and images using a wide range of colours. You have no restrictions on the number of colours used but as the compression ratio increases you will notice a deteriation of the image quality.
This format is becoming more and more widley used on the web as browsers now support it.
For more information on image formats please copy and paste one of these lines into a search engine :
- gif format web image about details explain
- jpg format web image about details explain