How to properly delimit multiple images before sending them over a socket

How to properly delimit multiple images before sending them over a socket

let's say I need to send, for instance, five images from a client to a
server over a socket and that I want to do it at once (not sending one and
waiting for an ACK).
Questions:
I'd like to know if there are some best practices or guidelines for
delimiting the end of each one.
What would be the safest approach for detecting the delimiters and
processing each image once in the server? (In C/C++ if possible)
Thanks in advance!