GIMP
When selecting a shape, GIMP indicates the area to include as white and area to exclude as black:
- After selecting a shape; choose "save to channel" to store it for later re-use
- To re-invoke the selection, hit "replace the selection with this channel" button to apply it
Furthermore, when the selection is activated:
- go to the "Tool Options" tab, click on "Move" under "Edit Mode" to re-position this selection
- or grab a "Transform Tool" from the top left screen corner, choose "Scale Tool" (Shift-S) then go to the "Tool Options" tab, click on "Path" or "Channel" next to "Transform" to specify which object we're using to re-scale the selection to any desired size.
Source: https://youtu.be/TRhqcaaD37k
