Sometimes pictures get relocated if they have been uploaded to the wrong grid square by mistake. This is often the case with images from the very early days of Geograph, when there was no or only scanned out-of-copyright mapping available.
Very occasionally, a (first) Geograph gets reclassified as a supplemental image* if there had been a clear error in the original classification.
Also rarely, images are withdrawn or vaulted for a long period because they weren't taken from a place with public access and the land owner has complained.
In all these cases, the next uploaded geograph (if any) will take the point, and if that was yours, then you'll find a miraculous extra point on your profile.
*From 11 May 2016 the Supplemental Classification is replaced by Image Type Tags:
see http://www.geograph.org.uk/article/Image-Type-Tags