It's because there is a gap between the http:

and the URL.

So make sure the URL doesn't contain a space when you copy and paste it.

<t>Well I thought of a game for this forum and it's a very fun and challenging one.<br/>
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Basically I post a picture of a flower and one of you have to guess it, the first person who gets it right posts a flower and the game continues.<br/>
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I put the image on download so you cannot cheat ...