Since my last post, where I talked about drawling a line with pixels in PHP, I have been looking at drawing circles. As it turns out, there are a few different ways to draw a circle, so I'll go through a few options here.
To start with, there are some built in functions in PHP that can be used to draw an arc, circle or ellipse as a filled in shape or a line. The built in function in PHP called imageellipse() that can be used to draw a circle. This is part of the GD library.