DSC.jpg files display as thumbnails only on T2 from Townky media server


Hi everyone. I have recently been successful in getting my HDR T2 to "see" my media stored on a QNAP server with twonky media enabled. We have a relatively new sony digital camera which stores jpg files named for example DSC0001.jpg, which I have stored on the QNAP. These are viewable via the Humax T2 but the image is displayed as a tiny thumbnail in the centre of the TV. Any other jpg files in the same folders are fine. Any ideas? I haven't yet checked the exact resolution of these files but there not small and I think we have set to use the highest def setting on the camera which is generating the images. Thanks
The only suggestion I have to make is that perhaps the images or the file sizes are too big for the Humax viewer to cope with, and maybe it only picks up an embedded thumbnail.
Thanks. This problems seemed to resolve itself with later pictures though the files I tried to access originally stil have the problem. The only thing I can put the issue down to is that the original files were uploaded to my home server via an eye-fi wireless sd card direct from the sony digital camera. I now have the eye-fi set up to go via an i-phone first and then onto the server, and those files seem fine on the TV.
I may be wrong, but I think loading photos onto the iPhone causes them to be optimised for the iPhone - ie down-sampled - to save memory space.