You surely must have seen it at some point. it is often used in many references to Yom Kippur services. Here is an image of the painting:

There is a lot of story behind this. The artist was a Polish Jew named Maurycio Gottleib in 1878. The painting is supposedly a scene of the shul from his memory after he davened in a shul in Vienna and then decided to immortalize the scene in a painting due to an antisemitic attack. Gottleib painted himself into the scene a few times, plus one of the women is his fiancée (who broke up with him) depicted twice. The Torah scroll is embroidered with a memoriam to himself, depicting himself further after death. There is a lot more and you are welcome to research different explanations of the art.

Another interesting aspect of this painting is the edited version of it, which is also popularly used. I suspect many are not even aware they are not looking at the original. The edited version of the painting has removed the women, or blurred them, surprise surprise, from the balcony. "The Jewish Encyclopedia" posted the following edited image on their page explaining Yom Kippur:

I guess everyone can write the history as they want it, so here is the explanation from Kikar, specifically about the edited version. I found the assumptions entertaining.

First of all, Gottleib was not frum, not God fearing, so he painted women, rachmana litzlan, into the painting! GEVALT! Not only that but he depicted the seen with the women in the ezrat nashim being visible with no curtain blocking the mens view of them.

According to Kikar, this being a hassidic "kloiz" in Galicia it makes no sense and Gottleib must have painted the curtain a couple of meters back form where it actually was so that he could include women in the depiction. 

Michlol is something of an attempt at being a frum version of Jewish Wikipedia for frum people who don't want to use Wikipedia (for tzniyus and apikorsus reasons, ostensibly).

There you have the story