Google: Vision API
Google Vision is a cloud based tool that gives accurate descriptions of images. The data returned is expansive, and useful in many different scenarios.
This means you can bulk process images to get data you need for analysis, or metrics. And as with all Google API, they are easy to work with.
I discovered this while looking for image data options, and ran several tests to check validity
Filtering community content, aiding with SEO, and masses of other great uses
It is hit and miss with complex, or unique images, so human moderation is needed