It was a picture of the second plane crashing into the WTC on 9/11, with a cartoon of a frog that might not technically be a white supremacist but that white supremacists have been appropriating as a meme for a couple of years, and it's a stereotypical-looking Jew, who appears rather happy about it. Plenty of far-right conspiracy theory peddlers like to insinuate that the Jews control the world, and are responsible for disasters like 9/11, or that 9/11 is a false flag hologram that was thought up by alien lizard Jews in control of the world to... I don't know, conspiracy theory logic never makes any sense to me.
It's pretty clearly a white supremacist meme, and you'd have to be pretty ignorant about the alt-right to not recognize it as their handiwork.