Tried adding the following image as a remotely hosted modification image.

Got an error saying it was an unsupported filetype.

I presume this is either down to the file extension being in capitals

(unlikely), the square brackets in the filename confusing it

(only likely if you're regexp matching on the filename) or it having a fullstop elsewhere in the filename?
http://theshado.ws/images/imoc/Rear/P24 ... 10[01].JPG