I use image viewer on the gnome shell. Yet when I am in file manager and open an image, the image opens in the background.
How to start in front of everything else?
This is intentional Gnome Shell behavior. The way this focusing behavior works is if you double click the image or right click and open/open from Open With, the shell will detect if the e.g File Manager is still in focus/on top.
Example, if you opened the image and then clicked back in to the File Manager in the 1-5 seconds it takes to open(perhaps to open something else), it will open in the background. If you have not clicked anything since you opened the image via either double click/open with/return then it will automatically open that image in the foreground. If this behavior is not occuring the Shell is either detecting the wrong activity inside of the File Manager, or something else is stealing focus. If this is the case you can do the following:
The best way to change this would be to use the Steal My Focus extension, it does not work per application but hopefully that will be possible in the future.
You can install it by clicking THIS and selecting the On/Off toggle switch, then accept to install. Once installed it should begin working automatically.
This should work on 3.2 as well as 3.4.
I think I found answer to that problem; it is the problem that appears with other programs also. I've solved it completely by configuring copiz appropriately.
Please, look at my answer to this question. Sometimes new windows don't come to the front when launched