Hi,
My Lumia 930 (running preview for developer latest built) firmware version changed in extra+info to denim but Lumia camera still doesn't work and says phone must be updated to denim first. Any idea what's going on?
It is not running a "fake" version of denim, it is running a older version of the firmware. Once the update is available for your device you will receive a notification, said update will bring your firmware version upto date. This latest update is a pre-requiste for the advanced features of Lumia Camera 5.0.
You can use the above link to check if the update is available for your device without waiting for the notification, you may need to look under carrier in the about screen to confirm which region your phone is locked to.
Checked support page and denim update still not released for my phone seems it was a bug as extra+info returned back after receiving an update to cyan again