If you are looking for a simple and efficient tool to capture custom shapes from your screen, this can be one choice.
Can save captures as .bmp, .jpg or .gif.
You can use different kind of shapes to take images from your desktop: full screen, active window (window of used application), rectangle, square, ellipse, circle or polygon.
Once you made the capture, you can edit the image before saving it: free hand draw, erase, pick color, fill with color, insert text, draw additional shapes and lines.
Even it looks basic, this software has a great potential to make your desired tasks and i was truly delighted when i have tested it.