Question: I sometimes daven in a shul hall where they have a big picture of their Rabbi on the back wall. Is this an issue?
Answer: The Gemara (Berachos 5b) teaches that one must ensure that there should not be any chatzitza, barrier, between one davening and the wall. The Beis Yosef (OC 90:21) explains that this does not apply to furniture such as tables and benches, but to wall hangings and pictures that may distract one in their tefilla. Therefore, Rambam (Teshuvos 215) writes that this applies equally to paintings on the wall. One who finds themselves in front of a picture should close their eyes or look into their siddur while davening (See Shulchan Aruch OC 90:23; Mishna Berura 90:63).
The Magen Avraham (90:37) adds that one may paint onto the wall that is high above one’s heads where it will not disturb anyone davening. The Aruch Hashulchan (OC 90:28) defines this as three amos.
The Tur (YD 141:14) writes that one should be careful not to include pictures of animals in a shul as one may get the wrong impression that one is bowing down to them. R' Moshe Feinstein (Igros Moshe YD 2:55) writes that the minhag to place a picture of a lion on the aron hakodesh is acceptable. Nonetheless, the Aruch Hashulchan adds that this prohibition is particularly true with pictures of people.
Nonetheless, the Mishna Berura (ibid.) notes that this is not strict halacha, and if one is in a room with pictures, one does not need to find a different place to daven.
In conclusion, one should not place pictures of people in shuls. One may daven in a room with such pictures hanging, particularly if one is not facing them. If one is facing the picture, they must try to close their eyes or look into their siddur while davening.