Can you give me an example, because I tried it and it didn't work.
Sure.
1) Google image search: Dog. Results:
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I'll be using the third picture for this example.
Clicking on that picture and then asking to see the full-size image gives me this URL:
http://www.harlemfur.com/images/Dog_Olive.jpg 
2) Uploading the picture:
Here is my picture before-
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Now I'll go to insert the new URL to be uploaded:
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3) Finished:
Now I just go to Change profile at the bottom and it's finished:
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-OR-
1) Selecting a photo from my computer:
I selected this picture to use as an example:
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2) Uploading to imgur.com (
http://imgur.com):
Open the website and follow these steps:
Click to upload from your computer-
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From there you'll have to locate the file you want to upload from your computer. When you're done uploading it will take you to a page like this:
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Copy and paste what it has directly below "Direct Link (email & IM)" - this is what you will be uploading to the forums.
3) Uploading the picture to the forums:
This is the same thing that I did in the second step below the Google Image Search method except I'm now copying and pasting this new link in place of the old one:
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4) Finished:
After clicking Change profile, my new Profile picture is as follows-
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And that should do it. Remember, if the URL you're using does not end in .png, .jpg, .gif, etc. then it will never upload. Try to find a URL that has one of those endings.