@alantig sums it up pretty well, but I think PRS is missing a marketing opportunity by not hosting the pix. Yes, liability could ensue when someone posts something out of line, but a properly written TOC would avoid the legal thorns of all of that. As for cost, storage gets cheaper every day and I guarantee that the cost of hosing pix from members would be tiny (like less than $100/year type tiny - 8TB drive could hold 20 million pictures at 50kb/pic). Then there is also the cost/complexity of "monitoring" the content. Who is going to take that on to ensure unwanted material is not posted and if it is, to remove it. But back to the marketing opportunity. What could be better than your customers fawning over and flaunting your product? With the TOC in joining the forum, they could put in a clause saying that if you choose to post here, you allow PRS to use those images in any way they wish (other than sale thereof). Then ad campaigns for the company could utilize some of the great photos that get posted by forum members. Opportunity lost IMO.
I have been a computer programmer for 30 years. In the early 00's, I built from scratch for clients, forums similar to this that included the ability for users to upload photos, pdf's, etc. But when I joined this forum in Feb 2021, I was thwarted in my efforts to post pix, even though I was using my own hosting service. The problem was secure websites must be used. So no http://, it HAS to be https:// for all users to be able to see it (which is in part based on users browser/system settings). When you go to put in your URL of a photo, you will notice it suggests to put http:// at the front of your url, yet that DOES NOT WORK as it MUST be https://. Once I figured that out (it allows you to post it with http but then many users will not be able to see it), I applied to my hosting company for the secure certificate and was able to get that added to my account at no extra charge, but an added wrinkle to "not only will we not host your pix, but they must be hosted at a secure site". You also have the issue that the URL you give pointing to the picture ends with a supported image extension (.jpg, .gif, .png, etc.) which is why google drive does not work. There are some BB Code ways to post pictures, but that is NOT using the forums picture inclusion method.
Anyway, I get their position, and I get the users position which is why I and many others have written
tutorials (that link has my tutorial as well as links to other tutorials I am aware of on the forum regarding this topic) on how to do this at this website. It is a free forum (as are all other forums I am a member of), but if you want to play the game in full here, you have to reach to another service (and maybe even more services to get https) to make the experience whole! Is what it is, so take off your shoes, set a spell, y'all come back now, ya hear!