compare two blob colomn values to find percentage of similarity

Question

how to compare two blob colomns on the same table ? For example: PIC1 contains a picture of a bridge taken from 5 meter distance, whereas PIC2 contains a picture of the same bridge taken from 10 meter distance. I want to compare using query to show that these two colomns have X% similarity. If this X% is not met, then i flag the record as "not X% similar". is that possible to do it via query ? if not, what kind processing do I need ?