My book Custom Controls Library contains the source code for 101 custom ActiveX controls, including one named PicturePopper. This control is a PictureBox that animates the display of a new image in one of several ways. For example, when a program sets the control's Picture property, the new image might slide over on top of the old image from left to right.

This program demonstrates an ActiveX control with several different transitions, mostly written by Neil Crosby. They are generally easy to understand (see the code). They use PaintPicture to move pieces of the new picture onto the old one.