in reply to Copy files around network

On machineA, there is a folder where images are constantly updated.

It sounds like this might be the crux of the problem. Why not have this "folder" on MachineB instead? Then MachineA could remote-mount this via sshfs or similar and the image capture procedure can carry on, wilfully ignorant that it's really writing to MachineB. Does this solve the problem for you?