Upload pic onto a webserver which allows remote linking, and then click that fourth button on the second row in the post reply window, that one which looks like a pic with a landscape. Then a line like this will appear:
[img*]URL[/img*] (without the stars, i used them to keep it visible)
Replace "URL" with the http address of that pic.
There is no real 'nid pic forum here, but you can post them either in the painting forum or in the 'nid forum.
jwu