An HTML image is a table with single pixel cells that form a picture with their bgcolor property. Although the images are not practical, it can still be fun to create one just for the sake of trying it out. Basically, you make a table with cell padding, cell spacing, and border all equal to zero, then give each cell a bgcolor attribute and fill in the appropriate value.

Potentially, someone could write a PERL script or C++ program that generated patterns for shading areas, similar to photoshop's fill tool. I never got beyond making a simple program that took command line input and used it to determine which of about 5 colors to display on the screen.