Finding and matching SHA512 Unsalted Hash
A brute force search is probably impractical with your resources.

It appears that a CPU-based SHA-512 implementation might be able to do 2,000,000 short hashes per second per core (the figures I have are a bit slower - I'm assuming things will get a bit faster)

Given $32^{16}$ target images, that translates to approximately 20,000,000,000 core-years to search through the entire list (or about have that to get a 50% chance of finding it).  If you have 1,000,000 volunteered computers, and each computer has 10 cores, that translates to an expected time of 1000 years to get to a 50% chance of finding it.

A quick look at GPU performance looks a little closer to practical; however you'll still need millions of dedicated GPUs to get the time down to a practical level.

About the only way to do it practically would be to go with FPGAs or (better yet) dedicated ASICs - either approach would appear to be out of scope for what you have.