I've found that sometimes, it's necessary to hover the mouse cursor over an image or text box to see it clearly, but knew of no way to copy the enlarged section rather than the whole page with PrtSc.
Same problem applies with highlighted or selected text in documents, menus, etc.
I've just found a way in Microsoft Community, and it works:
When on the relevant page, click to open the Snipping Tool, then press Esc
Hover the mouse over the box/image to enlarge it, and press Ctrl+PrtSc
The snipping tool will then reactivate, allowing the usual method of snipping.
Same method works with highlighted/selected text, menus etc.