I'm starting to explore ArcGIS Online as my first introduction to web mapping (perhaps not the best choice of cloud services but thought I'd give it a shot). I was intrigued by their discussion of "story maps" and wanted to create one that overlaid raster imagery that I had on my system. However, I can't figure out how to add raster data. It seems to only accept .shp, .csv etc. I can add rasters if they're converted to layers, but can't seem to actually overlay them on the map. In looking through the help it seems the option is using a map service, the more I dig into this the more complicated it seems.
Is it not possible to simply overlay raster data as one would do in ArcMap Desktop?