A method includes matching at least portions of first, second signals using local self-similarity descriptors of the signals. The matching includes computing a local self-similarity descriptor for each one of at least a portion of points in the first 
signal, forming a query ensemble of the descriptors for the first 
signal and seeking an ensemble of descriptors of the second 
signal which matches the query ensemble of descriptors. This matching can be used for image 
categorization, object classification, object recognition, 
image segmentation, 
image alignment, video 
categorization, 
action recognition, action classification, video segmentation, video alignment, signal alignment, multi-sensor signal alignment, multi-sensor signal matching, 
optical character recognition, image and video synthesis, correspondence 
estimation, signal registration and 
change detection. It may also be used to synthesize a new signal with elements similar to those of a guiding signal synthesized from portions of the reference signal. Apparatus is also included.