The picture you have posted is ridiculous. The B-52 is a defenseless large duck in the sky. Even Vietnamese Mig-15 had shot it down. Iranians have Mig-29's and the specially anti B-52 weapon which is SA-5 operated by Iran with a range of 450 kilometers. B-52's will never come to Iran. B-1, is not used anymore for military operations and are limited in number and are also vulnerable to SA-5 since despite their reduced radar cross section are not stealth and have pretty much the same fate in a contested air space as that of B-52. The only plane that probably can make it to Iran is B-2. And US has only a few of them. They are slow, relatively low flying and defenseless with no radio emissions that is no radar and no radio communication while in enemy territory. Basically they are on their own and only fly at night so that they can not be observed. Iran has currently one weapon system which can shoot it down that is Tor M1 which uses optical search and tracking. But if Iranians invest and research on new low frequency radars as well as other novel systems. Lets not forget Serbian used a 1950's radar to bring down F-117. Iran should be able to do better if they invest more in research. And additionally B-2's have limitations. If a fighter plane comes to visual range of a B-2, then the B-2 is dead. Even a Mig-17 fighter would be able to down it easily. And B-2 stealth breaks down in rain and moisture so it would start to glow on radar screens like an Air bus. So it is not like B-2 is god.
Additionally, even some ordinary cell phone technologies with a software can detect B-2. Stealth is only effective against technologically incapable nations. Those even with little minds can find ways to beat it. So much so for stealth:
Electronic Aviation - Articles - Can Stealth Technology be Penetrable?
PS. If Iran can down RQ-170 which is the same as B-2 from radar perspective then they probably can do the same to B-2 as well.