For the record this has been in progress for a while. I just saw your comment when I came back here to add the findings to the thread. Thank you for at least looking at things.
The research was actually the simple part. The great effort was in getting confirmations from large amount of artists that they didn't give permission for their art to be used. But I think that it was necessary to avoid a different kind of pedant commentary -- the "Well, are you sure the art was used without permission? Couldn't the people behind the sites have contacted these specific artists?" kind of nitpicking. And now I've spoken to enough artists whose work was taken to be very sure about the scale of art theft.
But in any case I'm not the developer of Wigglypaint and have no sway over the license. I'm just an artist and community member who noticed that the creative works of people here on itch being were used as materials to scam people elsewhere and I really didn't like that.