Wikipedia also cites an entry from the Hartmann Lexikon, but that website seems to be down at the moment.
It's notable that there simply is no corresponding Wiki page in English, which suggests that a single term may indeed not exist.
The problem I have with 'miraculous statue / image' is that it sounds as if the physical object itself appeared or came into being in some miraculous way, like with a poof of smoke as if conjured up by a genie. In fact, as I understand it, the images are not themselves miraculous; they are real works made by human artists. And they don't actually do supernatural or magical things, so they're not 'miraculous' in the sense of miracle-working either; they just exist as a focus of prayer or worship, an object of reverence and devotion.
The prayers may often be prayers of supplication -- for miracles, perhaps, sometimes, but also just for help or understanding? Is 'eine Gnade' in the sense of an act of grace always a (big, amazing) miracle? Could it not also be just a modest sign of mercy, grace, favor, etc.?
And could these statues not also be the focus of prayers of thanksgiving, or commemorations / remembrances of other acts of mercy or grace?
So 'miraculous' seems not only misleading in its meaning, but also possibly too narrow in its focus. Which might explain why we're not really finding a lot of collocations with it in this context, even though there may be some.
Again, I'm just not sure there is a single term in English, apart from more general ones like figures / images of saints / of the Virgin.
Wikipedia links to terms like 'cult images,' and while that's probably a very accurate term in a context like anthropology or comparative religion, the average modern person on the street might misunderstand 'cult' as pejorative. So even there you would need a paraphrase or explanation, like 'images used as the focus of worship / adoration,' etc.
I'm not Catholic, but I sort of thought that was basically true of most or all images used in
Catholic worship and ritual. So I guess I'm still just not entirely clearly on why some religious images would be called Gnadenbilder, and others not. What technically defines a Gnadenbild, as opposed to, say, a Heiligenbild; or is it just another synonym used roughly interchangeably with other similar terms for such images?
That is, is this by any chance one of those instances in which German just happens to have more than one word for the same (type of) thing?