Your portrait is found in a variety of levels. The first place this can be done is in the Red Wing level “Through The Glass Flooring” because it’s the first time you have all 4 dimension batteries at once. The portrait on this level is located near the conveyor belts on the bottom, in a room with a pathway leading back upstairs. In order to unlock this achievement, you must be looking at the portrait and switch into all 4 of the different dimensions. Below is a video showing how to unlock the achievement.
Another place to do this is in the Research and Development Lab in the Great Hall which you gain access to after finding your first blueprint tube.