I think Hologram limits a message size to ~10kB, there should be an old forum post about it (i’ll look through my history as well). This is a limitation of hologram cloud, not the underlying cellular network. Your options are to either split the data up into multiple messages or use a 3rd party cloud provider. Note you could setup an aws s3 bucket and http “PUT” the image in their directly. I have done this wither large-ish files.
Here you go: Maximum data size per message via Socket API