What are the terms and conditions you are providing these 'free' photos under please? You should consider it unlikely that a serious startup would use your photos based on 'genbit on HN said they were free - seems legit'.
Also, have you considered submitting images to sites like unsplash.com or skitterphoto.com, which basically offer the same thing but with a CC0 license?
And if it is just feedback you need there are plenty of photo communities online like Flickr where you can post images and solicit critical feedback.
It is a nice offer you make but posting something like this to HN is really limiting and cannot last long. I think you are better off looking elsewhere, so give it a try and good luck.