I use photobucket. Obviously, open a PB account and upload your photos. With the photo you want displayed, there is a panel on the RHS of the screen giving links to share this photo. Left click on the HTML code and it's copied (no need to do the usual right click/copy) then right click/paste into your post. The photo won't appear when you do this - just the HTML code, but will be visible once the post is posted.Be aware that it will give everyone access to all the photos you have for that account on PB (I think) so best not to have pictures of the girlfriend in the buff on there

Other online photo sites will be different. This procedure seems to size them nicely as well.

Classic C5 Euro 4 at the moment.
Also CBf250.