I'm using the Export Tile Cache tool in ArcToolbox to create a TPK file which is then sideloaded into Collector iOS using the methodology described here: http://doc.arcgis.com/en/collector/ios/collect-data/offline-use.htm
All this is working fine but I noticed that when using the Manage functionality within Collector to look at the TPKs that it shows a default thumbnail for each item.
It would be quite useful if each TPK could have a custom thumbnail image to help users distinguish between the different offline basemaps. If I poke around in the TPK file on a PC then I can see that there is potentially provision within the esriinfo\iteminfo.xml file for a thumbnail e.g. <thumbnail>thumbnail/thumbnail.png</thumbnail> but there doesn't seem to be any kind of workflow that I can find to actually set this to a custom image.
It's really not a major problem but thought I'd post just in case anyone else had cracked this particular nut.