How can I use power over ethernet to transmit data and power to the OpenMV Cam M7?
If your device uses only 100base-T ethernet, you can use the cheap and simple PoE protocol used by inexpensive IP cameras.  100base-T uses only two pairs of the 4-pairs in a standard cat-5 cable: orange &amp; green (plus their respective white-stripe conductors).  The otherwise-unused blue and brown pairs are used to supply power to the camera.  Most IP cameras used 12 Vdc as the PoE source.

This technique was specified in the IEEE 802.3 standard in 2003.  It is known as "Alternative B" and places the positive voltage on pins 4&amp;5 (blue pair) and ground on pins 7&amp;8 (brown pair).

You can purchase inexpensive adapters or simply roll your own.