My wife's 2+ year old, off-the-shelf Canon 7D takes 18 megapixel images. RAW file size is 20+ MB and it can shoot bursts of 12+ images in under 2 seconds. That's 120 megabytes/second (bursted) from consumer grade gear.
I imagine the CIA/DOD can afford much better gear that captures much more data than a single $1700 DSLR. I also assume one drone can carry multiple devices. As far as data transmission, I would bet that being loss-less and encrypted take much higher priority than compression.
I would love to hear the number for the total amount of data gathered by drones monitoring the OBL strike. Hopefully I will still be here in 50 years.