Read the effin' TOS
Right there, section 5, "Your Rights" "...By submitting, posting or displaying Content on or through the Services, you grant us a worldwide, non-exclusive, royalty-free license (with the right to sublicense) to use, copy, reproduce, process, adapt, modify, publish, transmit, display and distribute such Content in any and all media or distribution methods (now known or later developed)."
"...you grant us... license... to... modify... such Content in any and all media or distribution..."
Of course, with lawyers and adhesion contracts, it's white there in black and right, or what's left.