Why would an organization not accept a JPEG file uploaded from Dropbox?

gerry_51 wrote:

But it's not actually on my computer, it's out there in the Dropbox cloud, right? (It just appears to be on my computer ...

No, not exactly.

First and foremost, the Dropbox folder on your computer is a regular folder like any other, and anything in the folder takes up space on your local drive. It is not a cloud-based folder that only exists online. It's just a regular folder.

Now there are features available to make it so some of your files don't actually exist locally. Selective Sync can be used to remove entire folders from your local drive, but then you could only see and use them through the Dropbox website. Then there's the ability to mark a file or folder as Online-only. This is where a file appears on your computer but doesn't take up space, and only exists in the cloud. However, if you interact with the file in any way, whether it's to open it for viewing/editing, or even to upload it to another site, the file has to be downloaded back to your local drive by Dropbox before you're able to interact with it.

So, even if you marked a file as Online-only, Dropbox would have to download it back to your local drive before you could upload it to another website, and that website would have no idea that Dropbox was involved at all. To your browser, you're just grabbing a file from your local drive and uploading it.