I have published a map service using imagery of the type EMF and PNG using ArcMap having picture symbology for layers. The EMF show up as BLACK DIAMOND Symbol while the png format images show up perfectly attached screenshots.
Had the same issue, Fix was to convert to a PNG and then re-publish. ESRI Docs says that *emf should be used for performance, but I am scratching my head as a PNG in some scenarios can be smaller in size?
