The height of screen shots in VLC 2.2.4 is slightly higher than the actual height.
When taking a screen shot of a 1280x720p video the image size is 1280x738.
The image size of a 1920x1080p comes out as 1920x1090.
The problem effects both the Windows and Linux versions of VLC 2.2.4 so it's probably common to all versions of VLC.
Tested on Windows 7 (64bit) and Opensuse 13.2 (64bit).