Why do not you send ETX ( Hex - 03) end of transmission flag to indicate that image is completed.
That won't work - binary files can contain any byte sequence as part of the data.
You should implement a simple transmission sequence, like: 1) send # of images (2 bytes), 2) send size of image #1 (4 bytes), 3) send image data #1, and then repeat steps 2 and 3 as many times as required.