How to ignore the excess blank part around images in 2D?

Hi! I am making a simple project, with a clickable map. The map contains the countries of Europe, and it is constructed from all of the countries cropped out of a map, put in a ui image, the rearranged in the desired shape. When I try to make the clickable part, some countries couldn't be reachable because of overlapping transparent place around the special shape of my sprites. Is there any options to mask, or crop the excess part out, without too complicated code work (like checking if every part is not transparent)?

I know that in the attachment a simply put Ireland on top of the UK would solve the issue, but it is not just that simple in every case. It is a simple example of the problem.

Thank you very much for your answers!