Rav Ephraim Greenblatt (Rivevos Ephraim 4:3) says he was asked if it is permissible to hang photographs of Gedolim on the walls of a Shul. The Mogen Avrohom (90:37) says that you may decorate the walls of the Shul with pictures as long as the pictures are higher than height of a person. The Machatzis HaShekel explains that since when a person davens he must look down, there is no danger of decorations distracting the davening at this height.
However says Rav Greenblatt there is another issue involved since when the images are of people it may look like the mispalelim are bowing down to these people. He compares this to the psak of the Radvaz and the Chida who both say that you may not daven in front of a mirror because people may think that you are bowing to yourself.
If for whatever reason there is a problem removing these pictures from the Shul, at the very least, he suggests they should be hung from the back wall, behind the mispalelim. Revach (Photo credit: euphoriaart)
You picked on the right picture for this question as the alter bobover rebbi was the closest thing to a melech the rebbi was so full of ahavas yisroel that anyone tat came in his presence would feel like bowing down to him out of respect
why not use a picture of the rebbe, since the only pictures that hang in shuls are pictures of the rebbe ?