Because the tag has to start with the img in the squared brackets [ ] and end with /img in the same [ ] . You also have to have the www after http.
The link should look like [img ]http://www.your_isp.com/~your_log_in/file_name.jpg[/img ], except you will leave out the extra spaces within the squared brackets.
'73 280SEL 4.5 (9/72)- RIP
Only 8,173 units built from 5/71 thru 11/72
'02 CLK320 Cabriolet - wifey's mid-life crisis
2012 VW Jetta Sportwagon TDI...at least its a diesel
Non illegitemae carborundum.