Hey. I'm just finding the "http://" link to the photo and putting that inside the [img]your%20picture[/img] brackets. I've not found a way around the 'forum attachment quota' problem that seems to be limiting uploaded pictures if that's what you think.
For some websites, like FB & Flickr, they make it hard to find out what the "http://" link is. Usually you can just rightclick on the picture, click 'copy' and then 'paste' it into the address bar (where you type web addresses in) and that will then open the link and display only the picture itself. I use Safari on a Mac and that lets me just drag the photo into the address bar rather than faff around with copy&paste (plus Macs don't have a right mouse button). Again this opens a new webpage with just the photo on.
Eg. copy and paste this into the address bar - http://farm6.staticflickr.com/5456/9223 ... 5661_z.jpg
For more problematic websites like Flickr I use the drop down menu 'View' in Safari and click on 'view source code'. This brings up the html for the whole webpage. From there I press 'CMD+F' (or 'control+F' on PCs I think) for the 'find' function and just type ".jpg" to scan through the files for pictures on that webpage. Sometimes there are loads so a bit of trial and error is needed. Some websites have thumbnail pics as well so it can also be good to 'find' for 'fullsize' as this is sometimes used in the picture file name.
I'm sure most internet browsers have a function where you can view the current webpage as html and it's not something that can only be done with Safari.
Hope that helps and is not too patronisingly put and actually makes sense.