This bit of silliness is so lacking in evidence, based on a weak coincidence, that it really is a bad joke. But since huge numbers of people are easily influenced by this kind of garbage, let's take it apart, bit by bit :
EASTER : You mean the annual feast of Christians celebrating the resurrection of Jesus from the dead?
WAS ORIGINALLY : You mean the first time (originally) that Christians got together for a feast called Easter, it had nothing to do with Christ, but was instead a feast to celebrate the Babylonian/Assyrian sex and fertility goddess Ishtar? If this is true, how could these Christians have been Christians at all? What made them Christians in the first place if the Easter they were celebrating was a feast of Ishtar?
What evidence is there that the early Christian worshipped Ishtar? Do we have religious art in the catacombs depicting early Christian worship of Ishtar? Early Christian writings talking about early Christian worship of Ishtar? No?
Funny, because we have early Christian art depicting and writings talking about the worship of Christ, and His rising from the dead. Long before Constantine.
No, the evidence is clear that, from the beginning of Christianity, Christians believed in the resurrection of Jesus from the dead. Early Christianity had nothing to do with Ishtar.
AFTER CONSTANTINE DECIDED TO CHRISTIANIZE THE EMPIRE : He allowed Christians to worship freely; to worship Christ, and celebrate His resurrection - something Christians had been doing for almost 300 years already by the time of Constantine.
EASTER WAS CHANGED TO REPRESENT JESUS : What's the proof of this statement? Can we find an official document showing us that Constantine said, "I am changing Easter." None?
The statement is that Constantine "changed" Easter; he didn't "invent" Easter. So there was an Easter prior to Constantine. What was this Easter? The worship of Ishtar? By whom? By Christians? That doesn't make sense.
Oh, by other people? The pagans? Then why "change" Easter? What is there "to change" if Christians had already been celebrating the resurrection of Jesus? The poster would make a whole lot more sense if it claimed that Constantine prohibited the worship of Ishtar, and compelled everyone to observe the Easter of Christians. But Constantine did neither, as well! What he did do was allow Christians, and any others who worshipped differently, to practice their religion with freedom. Edict of Milan, in the year 313.
Later emperors - not Constantine - waged a war against pagan worship in the Empire. But there was never a question of changing a pagan feast called Easter from the worship of Ishtar to the celebration of Christ's resurrection. Christians have been honoring that resurrection from the beginning.
ISHTAR - EASTER
The whole idea in this poster is based on a flimsy coincidence between the name of Ishtar and the Christian feast Easter.
It's a flimsy coincidence because "Easter" is merely the common (not official) English name of the feast. Constantine never called Easter "Easter." Constantine was not English. The Greek and Roman Christians during the time of Constantine called Easter "Pascha," as the Greeks do today and as it is still known in Latin in the Roman Church.
Again, it's clear there is no connection between a pagan goddess from Babylonia/Assyria, and an old English word "Easter," many miles away, with the Greek and Roman lands lying in between.
The official name of this feast, no matter the language, is the "Sunday of the Resurrection of the Lord."
OTHER UNPROVEN CLAIMS
That Ishtar is (or was) pronounced Easter. Scholars have studied the Babylonian writing system pretty well, and they all say Ishtar sounds like, well, Ishtar.
That eggs and bunnies were her symbols. From ancient art depicting Ishtar, we can actually say what were her symbols, and eggs and bunnies never appear among them.
Eggs and bunnies are symbols of fertility, which means life. Christ rose from the dead. No surprise then, that Christians, in an informal and unofficial way, used earthly, known symbols of life and fertility to express their understanding of the Easter event.
Ancient Christians used different symbols to represent the resurrection of Jesus (and of ours, one day). The peacock was one such symbol. Folk belief was that the skin of the peacock never decays. The peacock sheds its feathers once a year, only to grow more beautiful ones. Christians saw this as a kind of resurrection - falling away only to bring forth a more glorious life.