Do you mean a picture as in “Here’s me down the club last night having a great time” or a picture as in an avatar of the commenter ?
If it’s the latter:
http://www.gravatar.com/implement.php#section_2_2
If it’s the former, you’ll need to find a php uploading script and either have that supply a url which they can paste in, or otherwise incorporate it into the wp scripting.
A different approach may be look into some sort of gallery software which will allow users to upload pictures to your space ?
more like heres a jpg of wht i worked on ??
http://gallery.sourceforge.net/
“Give accounts to your friends and family and let them upload and manage their own photos on your website! “
I don’t use it, but it’s highly recommended I read.