I've recently (within the last two years) started collecting paper currency, mostly for the interesting artwork and designs. Don't have a lot of spare $$, so this was mostly visiting currency exchanges and buying the denominations I was interested in instead of buying the higher quality bank notes available online. This was going well up until almost a year ago for some reason. :O
I decided to continue my collection virtually, and started with high resolution scans of my bank notes. I continued with asking my various friends, family, and acquaintances for scans of any currency they might have. (Most had been tossed in a drawer for the last half year or so, but some actually quite good quality.) I got to the end of that road a while ago. (Currently 167 unique bank notes.)
I had some difficulty determining the origin of some of the bank notes, and it occurred to me the pandemic might be a good time to dip my toe into machine learning, (I'm a software engineer by trade, so it wasn't a stretch) so I started processing the scans to see what was possible. I eventually made a simple 'Not Hot Dog' app on iPhone that seems to be about 95% accurate, at least with my limited collection.
So, back to the topic of my post. I'm looking to get more high resolution bank notes, both to expand my collection and train on my neural network. I have no plans currently for publicly releasing the app, as its more to get my toes wet, but if others would like to try it out, I'm more than happy to let you beta test it, and if there's enough interest, I'd be happy to release it as a free app on the app store. (Perhaps an android version as well.) I have a full time job though, I have no interest in turning my enjoyable hobby into another job.
I'm also more than happy to exchange virtual notes from my collection with anyone else interested as well.