A normal camera can capture a rectangular image. If human eyes watch an area, what's the shape of the captured region? Rectangular? Half-spherical?
The capture area of the eye is a bit fuzzier and harder to define than that of a camera.
A camera captures consistent, fully detailed data right up to the edge of its sensor, and no data at all beyond it. Captured data is clipped by an ideally uniform sensor, augmented a bit by the lens, and is well-defined during design and manufacturing.
The eye can capture higher "resolution" near the center of its capture area and also has very little information about color near the edges (see also Peripheral Vision); so it's not quite as clean cut depending on your goal of "capture area". The eye also has a bit of a "blind spot" near the middle, which our brains basically Photoshop out. Additionally, it varies from person to person.
The effective capture area would really depend on your application (e.g. the "capture area" for, say, reading text, would be narrower than the area for, say, detecting motion).
Here is a typical diagram for a single eye, showing just the ability to see something in that area (does not show details related to peripheral vision quality):
Here is a typical diagram for both eyes combined, the solid white area is the overlap:
Both of those images are from a 1964 NASA report detailing aspects of the human visual field. If you want the detailed answer to your question and more, you probably want to take a look at that.
Note that our field of vision is very wide, those diagrams may not do it justice. As an experiment, close one eye, stare straight ahead and hold your arms straight out to the sides. Wiggle your fingers and slowly bring your arms forward until you can just see your wiggling fingers in your peripheral vision, and you will get an idea. As an added experiment, hold a piece of paper with text on it, and repeat the same experiment until you can read the text - this region will be extremely narrow and will give you an idea of how the quality of vision changes across the field. Also try with a colored object and bring it in until you can clearly identify the color.
There are also some simplified mentions of it in wikipedia:
One eye captures a roughly circular area. Because we have two overlapping fields of vision for depth perception, between our two eyes we capture a roughly elliptical shape.