Photo Problem I need help

[Reiyu]

Hello I dont know where to go so i will make it quick!

My Father took some pictures of my younger sister's prom but it seems the pictures have messed up some how they are showing they are .JPEG but they are still slow short video's. I tried to convert it but it doesnt work. I tried to play it and take a snapshot of the part but the video is too short or it just wont open in video.
Just to let everyone know the photo looks like a normal photo in thumbnail in a folder but in any Image viewer it shows the picture tiled in the image.(meaning it is the same picture but there are many but they are all much smaller.
If anyone knows how i can get the pictures back to normal size or change it to a regular picture again post here or Message me. please and thank you!