I read that the max 7219 could be used as in input device too. Can it power an 8*8 array of photodetectors and send the signal back to a computer system. If not, what is a better alternative.
The Max7219 is digital. Photodetectors are analog. So No.
Also, MAX7219 does not send any data out that is related to brightness of light shining on the LEDs it is driving. Don't see how you'd use it as a detector.
Start with some reading: https://www.google.com/search?hl=en&source=hp&q=led+photodetector+circuit&gbv=2&oq=led+photode&gs_l=heirloom-hp.1.1.0l2j0i22i30l3.1600.5730.0.14810.11.10.0.0.0.0.290.1260.0j3j3.6.0....0...1ac.1.34.heirloom-hp..5.6.1260.PBCVgyScHLc
What type of photodetectors are you looking to use? Do you have them now?
I was planning to use the leds on the board itself. By reverse biasing them I was hoping that it would give me a good array of photodetectors
I don’t see that working with a MAX7219 as it multipexes at 800 Hz with no feedback, so there is no way to sync up at all.