PaintBrush for Mac

I use Grab to take snap-shot of my screens and save it as graphics file (tiff). Today I took one of my XCode screen. I need to add some highlight lines to it. Then I need a PaintBrush like application for Mac. I googled on web and found one quite similar as Windows PaintBrush. It is also called as Paintbrush 1.1 and it is an open-source one.

The application is quite like Windows one. However, if I choose a image size in small scale, and tried to paste my Grabed one, and image does not automatically expand to the original image size. The Windows one handles this very well. Maybe I have not used Mac Paintbrush very much or maybe the new one would enhance this pasting feature.

I found another very good one: Seashore. It is also open-source code application. It has layers. I have not got much chance to play it. I think it should be very good one.

By the way, when I Grab a screen selection snap-shot, there is a window with information about the size of selection. I could use it to create a new graphic file. I tried to paste to Seashore. It does not crop image and I can move the image if the size is smaller than the original one. However, it does not have Windows Paint feature as well.