Hi!
You can use Qwatch in two ways:

• As a tool
• As a script

To use it as a tool, select an image and a shape, then draw over the image.
The image's colors will be used as a live swatch and the shape will be your "brush".

To use it as a script, select an image, a shape and a blank path (no fill, no stroke).
The image's colors will be used as a live swatch, the shape will be your "brush" and the blank path will be used as a draw path.
Double click on the tool button (in your toolbar) to set some preferences.

Have fun.
Read more here.
Video demo here.