Replaced image is resizing

[JohnM-UK]

I replaced an image on my gallery because I wanted to add a watermark. I added the watermark in photoshop, and saved the jpg at a size of 768 x 1024. I browsed to the folder where the image was located and just uploaded a new version of the image that was there (same file name so it replaced it). However for some reason the replacement image is displaying at a size of 899 x 1200 pixels on my gallery, where the original image is 768 x 1024. This applies for the image on my pc and the same image that is in my uploads folder.

My Gallery:
http://www.oneuk.f2s.com/photos/index.php

The image in question:
http://www.oneuk.f2s.com/photos/displayimage.php?pos=-96

Screenshot of the original:
http://www.oneuk.f2s.com/images/temp/folder.jpg

The actual image on my ftp in the gallery uploads folder:
http://www.oneuk.f2s.com/photos/albums/uploads/N_DSCF2254.JPG

[Nibbler]

Use admin tools to correct the file size information for that album.

[JohnM-UK]

That didn't work. All that did was reset 'views' to 0

[Joachim Müller]

Well, you should have ticked "Update thumbs and/or resized photos" in the admin tools, not "Reset view counters"