{ "message": "No converter for making <plone.namedfile.file.NamedBlobImage object at 0x7fbf29b7c488 oid 0x7daac in <Connection at 7fbf372850d0>> (<class 'plone.namedfile.file.NamedBlobImage'>) JSON compatible.", "type": "TypeError" }
After some googling, it looks like the only workaround for this is to use @id and append /@@images/image/my_scale
About the 'additional notes', I just want to mention (in case someone else runs into similar things'
If you (accidentially) name a field the same as an existing (lets say you add a field 'location', this will happen
a) If you request 'fullobjects=1', you request will include the field 'location' (with the value from the 'new field'.
b) If you request the field by using 'metadata_fields=location', it will return 'null' (unless you have also set the 'original field', I assume)
If you use a 'Choice' widget, this happens
a) You use 'full objects' and you will get field, and use your value by myfield'['token']
b) You request 'metadata_fields=myfield" and you only get the value 'in return'