Try saving them in a lower resolution (say max 50Kb per image). Higher resolutions often result in digitis.
The answer could be down to the size.
Another is a site like this requires pictures to be posted via a hosting site such as photobucket, and to be able to provide the link with which you can post onto a forum, they have to use various methods of compression, which will result in a loss of quality.
The one I just authorised look a bit grainy - was it a cam pic???? Find some are like that if it was...
The two public ones on your profile look ok (well, they look better than ok :rascal: but i mean ok in technical terms ) a bit grainy so i'm guessing you're using a webcam or a mobile phone. If this is the case try using more light to get rid of the grainyness.
If the ones in your private gallery are blocky, make sure you'v uploaded the picture and not the thumbnail or used the wrong link in Imageshack.
Feel free to send me a PM if you're still having trouble