There are four types of symbols that the Image Navigator can contain:
A Picture is a vector-based drawing that can be stretched without distortion. Pictures are implemented using a Windows metafile (*.wmf).
A Simple Picture is a Picture that has only one fill color and one line color.
A Bitmap is a pixel-based drawing that looks best at its original size. Stretching a Bitmap can result in a jagged, distorted image.
A Texture is similar to a Bitmap, except you can tile it to form a never-ending pattern.