The latest version of Digital Photo Professional has introduced a feature that I really can’t think of a use for, circular crops. What’s more the way it works is a little strange.
A circular crop of an image makes sense if it’s to be framed and used with a circular mount card, also if the image is to be used for printing on a printable CD/DVD, since most of the Canon PIXMA printers can do that. So you open the image in DPP, select the Trimming / Angle Adjust tool from the menu and then from the presets choose Circle at the end of the list. You can adjust the radius of the circle, and also move it around the image. Take care with the edges of the image since the circle can be moved out of the image resulting in a circle with a flat edge.
The implementation in DPP makes it hard to use since when an image is processed out from DPP with a circular crop it gets a black frame over the rest of the image. Looks like the people who created this want to use all the black ink in your printer, especially as the image is not even trimmed to a square format as seen below.
To update to the latest version of the Canon Digital Photo Professional Software you can get the updater programs from Canon for both Windows and Mac computers.