You might want to research the Screenshot activity in a bit more detail.
It has an option named Clipping Region.
You maybe able to come up with the rectangular area you want to clip based on your screen resolution.
Target.ClippingRegion - Defines the clipping rectangle, in pixels, relative to the UiElement, in the following directions: left, top, right, bottom. It supports both positive and negative numbers.
Also, the Marketplace has a Clipping Component created by UiPath for this purpose. You might want to search market place . But this might help you if your automation is attended.
Hope this helps.