Recently, myself and other members have not been able to upload photographs.
Nothing has changed as far as the software goes, but I get this everytime I try to upload a photo, as do others.
Adequate file space on the server?
/data and /internal_data chmod 777 recursively?
What version of PHP are you on. If any of the 7.x lines, 1.4.x of XenForo does not support it if I remember correctly - you need to regress back to 5.6 of PHP.