The IPTC standard defines a set of fields that image software can write and read: who made the image, who owns it, a caption, and more. One of these fields, the digital source type, states whether a picture was captured by a camera, composed from several sources or generated by an algorithm.
That field has become the common invisible marker for AI-generated images. Marketplaces that do not allow a visible AI label on the picture point to marking in the metadata instead, and search engines ask sellers not to remove it. Herofab embeds the invisible IPTC marker for AI-generated media in every image.
Metadata can be lost. Screenshots, some messaging apps and export settings that strip metadata remove the fields, and with them the marker. The file submitted to a marketplace should therefore be the downloaded original or a copy saved with its metadata intact.