Here we go again...people taking pictures and presumably snapping ghosts accidentally. CLICK HERE and see the latest 'ghost' to be photographed.
There are many things out there that can be purported to be a ghost if you stretch your imagination...trees, bushes, shadows, etc. In this case I think it just may be the interior wall inside the castle door (concrete, wood maybe) that could be mistaken to be a spook. Click and see for yourself.
Pictures can include 'ghosts' if you twist your mind a little and stretch plausibility. Pictures can also be altered digitally & we can never really know if there are any authentic pictures of ghosts out there or not. I don't believe this make up your own mind.

London Stereoscopic Company/Getty Images