Open the Terminal window in Ubuntu (Alt + Cntrl + T) and type eog to open the image viewer program.
eog <name of the image file> // You can use tab to auto-complete the filename.
The Terminal will hold the access as long as the application is open and you would not be able to do much on the terminal. Thus you can have the control of the terminal you can run the application in the background using ” & ” at the end of the command i.e
eog test123.jpg & // This will open the test123 image file while you still have control of the Terminal.
Hope this quick tip was helpful.