There are many legitimate uses. Vendors have experimented with making canvas readback opt-in (with a popup) but I don't know if it'll ever ship because it simpl

There are many legitimate uses. Vendors have experimented with making canvas readback opt-in (with a popup) but I don't know if it'll ever ship because it simply breaks too many websites. Sometimes it's used at page load to generate variants of a single image to reduce file sizes, or used by games to prepare image assets before they start up.