In Photoshop, if you draw a Ellipse/Circle/Rectangle/Square and hold down the ALT Key, the starting Point is the Center of the drawn Figure.
Holding ALT+Shift should work also für Circles.
I think it's easy to implement and it is very helpful if you want a Circle around a already drawn Object.
The same for Ellipse/Rectangle Select.
If you want to Cut a Face it is easy to start with the Nose,
hold down the ALT Key and move the cursor to select the Face
with an Ellipse.
BTW it is GREAT WORK!
Yesterday i found your Program and now i will never use the original Paint again.