I'm not a lawyer, hence you may take my post with a giant grain of salt. But the Terms of Service states:
'You agree that by submitting any material of any kind to us (including but not limited to posting chat) for any purpose connected with any Jagex Product (for examples, suggestions and ideas for any game or contributions to any gallery page), you are giving us a non-exclusive, perpetual, irrevocable, worldwide, royalty-free license to use, modify, copy, publicly perform, publicly display, reformat, translate, excerpt (in whole or in part) and distribute such User Content for any purpose, provided that Jagex may not use User Content in violation of the Privacy Policy. You agree to waive any moral rights to the extent permitted by law and that you will not withdraw the submission or attempt to make a charge for its use,. Furthermore you warrant that you are the exclusive copyright holder in relation to the submission and that the submission in no way breaches the rights of any other person or entity.'