Example: See image https://commons.wikimedia.org/wiki/File:Lillsj%C3%B6n_2015.jpg
Under Metadata click on "Show extended details"
There it says:
Image height 4,608 px
Image width 3.456 px
It should be the other way around, i.e.
Image width 4,608 px
Image width 3,456 px
Suggestion from [[user:LX]] is that the code around line 177 in the file Exif.php, see http://git.wikimedia.org/blob/mediawiki%2Fcore.git/8dff5095da045442f257a2395c31216e1469bd71/includes%2Fmedia%2FExif.php#L177 might be the cause of this problem.