Some large images contain a smaller thumbnail which is a low-resolution version of the entire image.
This smaller image-inside-image is used by some programs, such as Windows Explorer when displaying the image in Icon View. Otherwise, to display the image's icon would require reading the entire image and converting it to icon-size, which would unacceptably slow down the display of the folder.
I'm guessing that Windows Photo Viewer is displaying this thumbnail in a user-friendly manner, while reading the larger image. However, that larger image is damaged, and only the thumbnail has survived as intact.
Recuva is a good photo-recovery program, so I guess that the damage is caused by your having over-written that part of the image. You should never write data to a volume that you wish to recover.
If, however, that volume is still reasonably intact, you can also try another very good file recovery product:
PC INSPECTOR File Recovery
but remember to copy the recovered images to some other volume, otherwise when recovering one image you may be destroying another.
For repairing damaged JPEG images see this thread : Corrupt jpegs, thumbnail extracted....
It recommends quite a few such tools, as well as thumbnail extraction tools.
ExifTool looks especially good.