Image comparison (edges/shape only, no color) - How to distinguish cat from cat with prey

What is the easiest open source implementation of an image comparison algorithm that can produce a similarity score for a black white picture / edges ?

It doesn't need to generic, i could teach it with a couple of images.

Backg开发者_开发百科round:

I am working on a cat flap, that only opens when my cat approaches without prey.

I found similar but dead project: Flo Control

Thanks for help.

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This field is known in the research literature as classification, and the algorithms as an "Image classifier". Googling for one of these phrases will give you lots of hits, and adding the words "open source" and your programming language will probably give you what you want.

WND-CHARM seems popular, but there are lots.

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PS, if you are using Java, you might find the following question helpful. Image Classification Algorithms Using Java