As a non-believer, let me give it from my perspective.
First, often the response when this topic comes up is the Eucharist. Not to denigrate the Eucharist, but let’s imagine a religion that both you and I consider untrue. If a practitioner of that religion were to perform a ritual over a container of water that showed no perceptible changes in any of the senses, and had no discernible alteration in effect when consumed, we would both be skeptical a miracle had occurred.
Second, if we take Mother Teresa’s canonization, one of the two miracles ascribed to her was the healing of a woman claimed to have occurred from an image of Mother Teresa. The problem is the woman was under strong medical care, leading the non-faithful to (I think rightly) chalk that up to a non-miraculous cause and effect. It sets the bar for what qualifies as a miracle embarrassingly low.
Third, even if there are a few that would not believe practically any miracle there are a great many that would be swayed. It doesn’t have to be all or nothing. And the reason why people rationalize alleged miracle is because there are very rational explanations. Take the case of a statue of Jesus in a Catholic church in Mumbai, India. Water was dripping – seemingly miraculously – from the statue’s feet. People were going to it and collecting the water believing it might cure the sick. A man by the name of Sanal Edamaruku investigated and saw that water from a nearby washroom was going along a ceiling beam via capillary action and into the nail holding up the statue. It then leaked down through the feet. For his troubles of keeping people from drinking toilet water he was charged with religious offence and fled the country.
In the end, I don’t think the massive decrease in miracles coinciding with the increase in cameras is a coincidence.