Backstory: Whenever I need a stock photo, I'll head over to unsplash, adobe stock or any of the other stock photo marketplaces. The problem is that all of the images are so over produced, they're easy to tell they're stock, over produced and almost too perfect.
Lately I've been using iPhone images for background images on websites and creative for ads. These are converting at higher rates and seem to resonate better with customers. The images are authentic and aren't perfect (overly photoshoped).
The Idea: A marketplace for everyday photos.
Deep Dive: Very similar to unsplash and adobe stock, you would build a marketplace for normal, everyday photos taken from iPhones. By lowering the barrier to enter the supply side, you're going to need to monitor the quality very closely. In the beginning you can manually do this but you'll want to use a crowdsourced mechanism to eliminate any lewd or poor quality photos.
Another key aspect is being able to accurately search the images. Since OCR is not perfect yet, you'll have to resort to crowdsourcing again. As to not rely 100% on your user base, you could build a mechanical turk verification system.
This mechanical turk system would involve taking responses from multiple turks and finding the most common answers. For example, when categorizing the images, you would ask 10 turks and only take categories that 8 have all selected. You'll have to build a way to weed out poor performing turks as well.
Validation: Unsplash made a name for itself with UGC (User Generated Content) but now their quality rivals that of adobe stock with nearly "perfect" photos.
Monetization: You would charge a monthly fee or download fee for each photo.
Steps to Launch: Pick one specific niche and go from there. If you're running a small startup, target the entrepreneurial life and upload a bunch of everyday photos.