First of all, it is a GNOME mockup because I have already done a elementary photo viewer mockup and I am quite happy with it, so I didn't want to start a new one.
So, this is Eye of GNOME (EoG for short), the default Image Viewer in GNOME 3. I think that it currently looks a tiny little bit ugly, so I decided to revamp it with a mockup. (Hopefully something like this will be implemented
Elements from left to right:
Back/Forward - Navigating through Images in a folder one by one
Edit - Edit the photo/image (like elementary)
Title - Title or filename of the image
Fullscreen - Go fullscreen and hide anything but the image
Zoom in/out - self-explaining
Share - Share with e.g. facebook or flickr using Online Accounts
Settings - Settings like Information about the Image, editing tags, "Open with blabla" and Options of EoG can be accessed here
Close button - Widget of GTK 3.10 and up (Header bar)
Pixel size: Size of the image in Pixel
Filesize: Size of imagefile in MB, or KB
Zoom in Percent: Currently zoomed stage in percent
Please tell me your opinion, it helps in improving my mockups!