Follow these steps...
1> create an account on http://www.photobucket.com
2> upload a photo there, as you do on other webs
3> you will see this page, when you will click that photo
(see I copied IMG url from there, and just pasted here)
its done, but if you want to add that photo in Spoiler, Copy IMG from there, by clicking that once, and in here, Click on spoiler button on Top, and just press Ctrl+V (paste)
If you want to add that photo to avatar, Dont copy IMG from there, Copy "Direct" line, ((2nd in that rows)) and paste that in "Avatar link address"