I saw this on some RAW images. I found that Vista didn't support all image types and had to convert them or use other viewers such as IRFANVIEW, Picasso or "others."
Photo Gallery is being a complete nightmare and yet again fails at doing basic functions. </rant>
The problem is that only a few selected images refuse to appear at all in Photo Gallery (thumbnails included). They are blurred and stretched to the point where it's 10x larger than it should be and the image is completely unrecognisable. This isn't a complaint that the image has a slightly wrong ratio... the picture is displayed as a mesh of colours.
There's nothing special about the images. They are JPEGs, and I have many other JPEG images that work corectly. I've tried redownloading them, but apparently Photo Gallery does not want to display them properly. I've also already tried a disk cleanup for thumbnails and that too has done nothing.
Finally, the pictures look completely fine in image editing programs such as GIMP and Paint, so I know that it's not a problem with the source. Even creating a wholly new image in GIMP (complete with cropping) does nothing and it still refuses to work in Photo Gallery.
For some reason, saving a new picture from the one in Paint works... but it takes a massive drop in filesize and looks like ****.