But does this work only if the image has already posted once? So for the first time you post the image you can't do that but if you do this with an image already posted this is possible? And is there a way to change it so that you can do the same already in the first post?

If I upload images for posting are they stored straight to TMO or only after posting them? If they would be downloaded straight to members own storage space without a need to post it the same time then I think it would be possible to make that small picture: go where you downloaded the image, open it,copy the url and voila! I think that would work.