Sure, keeping a picture of your Rebbe (not just any rabbi) might protect you – from sinning! And that’s only if you think of him looking at you, not some magical segulah.
A few weeks ago someone sent around a video/photo story about a person who parked illegally near a shul, and the rabbi thought he was going to get a ticket, even though he had a picture of R’ Shayele Keresteirer on his dashboard. After davening, the Rabbi saw that the ticket the guy got was mistakenly written to a non-existing address, and was so impressed that the ‘segulah of R’ Shayele’ worked! And then someone sent around the ‘Moifes’ to hundreds of people, including pictures of the invalid ticket with the wrong address.
Later, some smart person used the photo to look up the perpetrator’s license number on the NYC Parking Violations website, and discovered that the fool apparently parked illegally every day and got tickets. So he had 200 valid tickets, but the one time he got an invalid ticket, it was a miracle due to the picture on his dashboard? More like the inevitable occasional incompetence of the traffic cop.