Problem scenario
You want to copy a subarea of a copied screenshot (just like Paint in Windows). How do you copy a rectangle cropped selection of a pasted screen shot using LibreOffice Draw?
Solution
1. Open LibreOffice Draw and paste the image in.
2. Click on the square icon in the upper right. It is an image of a square with sides extended on the left upper and right lower corners like this:
Click that beige/orange square with an empty middle.
Now you can select a subimage by moving a blue symbol on the perimeter inward.