for example [ img ]http://www.coastercrazy.com/track_exchange/upload/PegasussCastle-ChetCoasta-s.jpg[ /img ] (take out the spaces between the []'s as already said
It also helps if you right click on the picture you wont, then go to properties. You should find a link within the box. Copy that link and paste it. You will know if you have the right link as it should end in .jpg (or any other type of picture file extension e.g .gif .bmp)
Final result should be
