Image processing using Gabor filter
Gabor can be used as a filter bank in order to extract texutre 
features from an image (or image patch).
To compare images (or patches from image) using gabor I would follow the following pipline:


compute a filter bank from the Gabor (different scale and orientation)





post process to create new feature. you can compute the energy, and first statistics measures on the filtered images.
now that you have a vector of features for each image you need some measure to compare tham. You can use simple L2, or fisher criterior as some papers offer Comparison of Texture Features
Based on Gabor Filters


Please also take a look at the following question that is simmilar to yours.