We hear that phrase from our new students every time. The reason is that the display block can't be the last block in the program.
When a program, running on a robot ends. the display shows the programs menu list, and your image is not visible anymore.
This is a companion discussion topic for the original entry at http://www.fllcasts.com/episodes/397-ev3-phi-display-block-as-a-last-block-in-an-ev3-g-software-program