I know that the resource manager is coming, but not sure it that's idea for sharing wallpapers. Does anyone have any suggestions on what third-party add-ons might work and/or if you'd use something like Resource Manager for this task?
Hey man I just want to give you a heads up, that you should have made this thread here: XenForo Questions and Support.
As for your question not sure maybe upload for something? (If this is not the answer then I don't know)
You don't even really have to do that, with images in posts...you can drag and drop it to your desktop, right click -> save image as, or right click view image location and drag and drop it to your desktop.