How to recognize if there is a signature in a known area using openCV?

I have an area where the signature can be placed. On the white space of the paper.

How would you come up with an idea to recognize if there is or not the signature?

Thanks

Solution

If it's just about detecting whether or not something is written in that field you could do a simple histgram approach to see if there are enough non-white pixels to make the presence of ink likely.