1. A method comprising: identifying a candidate region of a test image as potentially depicting an instance of an object; identifying a first region in an object image that is similar to the candidate region of the test image, the object image being different from the test image; performing a comparison of the first region with a second region of the object image, the second region known to actually depict the instance of the object; and determining a validation score for the candidate region based on the comparison, wherein identifying the candidate region, identifying the first region, performing the comparison, and determining the validation score are performed by a processor of a computer device executing instructions.