star - Image sets for testing stacking algorithms?

I am looking for sets of astronomical images for testing different kinds of stacking algorithms.

The idea is simple: if one has $N$ images of the same object, the signal-to-noise ratio of the averaged image increases with $sqrt{N}$ under certain conditions.

Where could I obtain data for testing?

PS. I would propose adding the tags "image", "ccd", "research", "signal processing", and "machine learning".