So, just to test things, I created a structured databin

foo = CreateDatabin[
  "Interpretation" -> {"Contact" -> "Image", "Object" -> "Image", 
    "Drape" -> "Image", "tContact" -> "Number", "tObject" -> "Number",
     "tDrape" -> "Number", "ID" -> "String", 
    "Experiment" -> "String"}]

I added an entry via its web form located here. Note that each image is c.a. 19Kb for a total of about 60Kb and change.

The resulting databin, with a single entry, is almost 4Mb - which seems like a totally crazy amount of overhead. Notice also that the creation-time is wrong for some reason.

I have gotten closer sending the data via a POST operation via Python, but, at present, the data is not interpreted correctly (e.g., as an Image ) but is, rather, stored as gigantic pool of binary crud. So... onward!

Do you happen to know if this is a WRI-imposed limit?

I'm getting closer- but

An interesting thing I just discovered- I can upload an image, properly, to the data drop from within Mathematica, but, if I try to use the Web API I receive the message:

"Your databin entry could not be added because it exceeds the 25 kb limit."

from the POST request.

So I'm guessing this is going to make things a little difficult for me, since my images are, generally, larger than 25kb.