After a lot of searching there looks to be a high demand for image tagging or image searching in Dropbox. From what I have read Dropbox had more robust image capabilities, then they were removed. Also, that Dropbox doesn't support metadata tagging because it doesn't work on all OSs. Which is a shame because Dropbox search is amazing.
Since Dropbox has integration with Google Cloud it would be great if (as a paid service) you could choose a folder in Dropbox to use the Google Vision API to define images like seen here:
Even if that metadata was only inside the web portal I think many companies and individuals would pay for that service (of course with Dropbox adding a percentage to the Google Vision cost). In a perfect world (without racism!), you would select a Dropbox folder you want to run the Image Tagging in, then Dropbox would display a dialogue of how many images you want to tag, as an example "5,432 images, do you want to pay $x?" and you would confirm the price and purchase. After confirming the purchase, Dropbox would display roughly when the tagging should be done then email you once the process is completed and ask if you want to do any more folders.
Cost to Dropbox, of course, is developer time which only you would know.
The benefit to Dropbox is once it is running, this is a new revenue stream that is relatively hands-off. As you may well know, it is easier to sell to the same customer several products than to attract new customers to one product.
Businesses and institutions with media content
Individuals with photos
Side note: I read a lot of posts on the Dropbox support forum asking for this feature. In several cases, the support agent said "I can send this to the development team", an "I have sent this to our development team" would be better service to your customers taking the time to share.