I generate Item Description-compatible ISO19115 xml files that are delivered with raster products. I would like to include a thumbnail that will be displayed when the user opens the Item Description for the product, but have not been able to generate a binary string that matches the ArcGIS-generated binary format for the thumbnail image in the xml file.
I manually generated a thumbnail in the Item Description by updating it to a png browse image of the raster, and examined the results in the xml. I then generated a base64 string from the same png image using python (and tried a few other platforms to corroborate the results). The base64 string does not match the one generated by ArcGIS (as displayed in the Thumbnail section of the xml). If I replace the ArcGIS-generated binary string in the xml with my base64 string, the thumbnail displays nothing but a red X in the top left corner (and the size/proportions of the thumbnail frame change).
Does anyone know how to convert a png image into the format that is used to generate the thumbnail string in the Item Description? Ideally I would like to use python to convert the image into the appropriate binary for inclusion in the xml.