GK430
First of all, the pic has to be on the internet somewhere already (ie on another website).
When you've located the image you want, right click on it and then click "Properties" in the box that opens up. This will show you yet another box with all the details of the image in question. the bit you are interested in is the "Address" line - eg, if you go through this process for the pic I posted in this thread you will see that the address line is:
http://www.caa.co.uk/srg/aircraft_re.../g-byzd001.jpg
Make a note of the address line.
To put this pic into your reply to a thread click on the "IMG" button (underneath the Message Icons) and then put the address details you made a note of earlier into the text box that appears. Click "okay" and finish your reply. All being well, when your reply is posted to the thread it should have your piccy attached.
Hope this helps - it sounds more complicated than it actually is!
Camaro