With current technology, is it possible to detect an object the size of a human in space?

Space is a big place. So it depends where in space you mean.
I can see my car parked in my driveway on Google Earth, which are satellite images. You can also see the tops of people in those images.

So if you consider a satellite orbiting Earth to be in space, then the answer is yes.

But generally speaking these satellites and the ISS are in low-Earth orbit, which means they’re not technically in space. They’re still in the atmosphere, just a very thin layer of atmosphere called the thermosphere, which does produce a very minor drag on orbiting objects. Above the Thermosphere is the Exosphere and then outer space.

We do have objects in outer space, including satellites for Sirius/XM, Dish and DirectTV (to name a few) which are in a geostationary orbit around the equator. These satellites are way out in space at over 22 thousand miles from sea level.

Up there, it’s harder to see people on Earth because it’s so very far away.

So the answer depends on how high do you consider space to begin. Yes, you can see people from orbiting satellites, but no, if you consider some orbiting satellites and the International Space Station to be in a thin layer of the upper atmosphere and you want to go someplace like the moon to look at the Earth. Probably from that vantage point you’d be hard pressed to see individual people.

Here’s a map of the atmosphere.