I’m calling the blob/bulk endpoint with 19 images and getting 500 back.
I can call it with less than 19 and it’s ok (breaking point somewhere between 11 and 15).
Are there any restrictions in place for this endpoint that I should know of?
The plan is to be able to push well over 100 images in one automation run.
Are you including the image data as well or are you just inserting the blob metadata?
When you get an error response, there is a “reqid” value in the error object → we can look that up for details
There is a general limit of 1000 items or 2MiB max request size, but that should cause a 4XX error
Here is an example of the error:
{
'type': 'Error',
'code': 'API_INTERNAL_ERROR',
'message': 'An internal error has occured',
'reqid': 'E9uBtow2MX19ZwDEi4eE'
}
That said if the limit is 2MiB then on average I can upload around 12 images per call, and in my case the complexity of doing it one request per image rather than trying to group and maintain the size limit etc si not worth the effort so I’ll just be doing one request per image.
Still would like to not get 500s! 
Your request error is indeed a “data too large” error, but it seems this is not directly reported to the client - this should be a 413 error
For images which are over 2MiB (with base64 overhead) you can upload the blob without “data” and then upload it directly as binary data to
/blob/upload/<id> (where <id> is the numeric blob id returned by the metadata insert, not the long one). This is limited only by maximum blob size (same as in the Testiny app)