What is better to use to determine the difference between images?

Question

Programming

What is the best tool to use to determine the difference between images?
Applicable in C#/ but can be C++ or GO/Python, etc.
There are images of different resolutions, 1440x900 500x900, etc.
There are duplicate images, but I need to determine which ones are duplicates, which ones are original, and which ones are clippings from the original.
Before that, I didn’t encounter such a task, so I don’t know where to hit, I tried to search on Habré, but it’s even tight.
Upd.
There are not many images, for example, there are 100 photos and you need to compare with each other. BUT, there are 200 such bundles. This is not work, but purely for myself :3
Add. question, I'm thinking of parsing sites for typing pictures, what can you advise, pushing images into a SQL / NoSQL database, I'm leaning towards MongoDB, or stupidly saving files and adding the path to the database.
Everything will take place on my PC (AMD FX 9590 / 8GBRAM / R9 280X)
Upd 1
Some kind of game, not samples, I found only msdn sample
the rest is a poop from 2010 :D

Answer 1

Here, as I see it, there are two approaches to use EMGU (openCV) or implement the algorithm yourself, as an option, use the correlation function or FFT, and you can also use neural networks. If there are a lot of images and the time for their processing is critical, then using C++ + OpenCv is more preferable, although it is more difficult, but the performance is much higher here. Well, as an exotic use for this DSP or FPGA

Answer 2

Perceptual hash? If you need to look for visually similar images.

Answer 3

https://pypi.python.org/pypi/ImageHash this is for the same
ones for clippings more difficult, there is often OpenCV, and
even see SIFT, this is an algorithm, implementations are different