Over water or in other remote locations, there is no radar coverage thus there is absolutely no information about the plane location except position reports from the pilot. Airliners have "ping home" systems that regularly send various info (including GPS location) back to the central company servers using satellites. However, the reports frequency varies from 15 to 90+ minutes and even 5 minutes is A LOT for a plane traveling at MACH 0.7. But even if the position reports will be timely and accurate, during the descend (after a catastrophic event onboard), the plane might travel tens of miles from the last reported position. Then, ocean currents can move the pieces even further from the last reported position (as it have happened with Air France plane pieces).
Lastly, ADS-B is not a solution for over the ocean position reports - the radio is not powerful enough to transmit data over the long distance (this is why we need to build so many ground stations in the US to actually use it). Not to mention, that ADS-B is not fully operational even in US.
I think they could look at satellites looking at that region at the time. There are satellites just taking photos and they probably have captured something.
...there really aren't satellites 'just taking photos' of the ocean. You might have a spy satellite taking pictures of a naval exercise. I think you are underestimating a) how vastly big the ocean is, and b) satellite capacity (most intelligence satellites are over land).
71% of the world is ocean. The ocean is vast, and most of it has very little going on. Last month someone washed up having been lost at sea for over a year, having only seen two or three ships (which didn't stop). A few ships in 13 months.
Lastly, ADS-B is not a solution for over the ocean position reports - the radio is not powerful enough to transmit data over the long distance (this is why we need to build so many ground stations in the US to actually use it). Not to mention, that ADS-B is not fully operational even in US.