Yeah, generally speaking for object detection - Scale, position, rotation: typically you can identify something based on 2 of these really efficiently (for exam

Yeah, generally speaking for object detection - Scale, position, rotation: typically you can identify something based on 2 of these really efficiently (for example, wavelets give you a transform that is sufficient for object identification under scale and position transformations in O(N) operations). If you'd rather have orientation identification (ie. rotation angle) and scale in that mix but don't care about position, the radon transform is nice and easy to work with. But beyond inverting 1-2 key transformations, one usually has to pay a pretty hefty computational cost which often precludes online (near real-time) use.