How many "pixels" the human eye captures does not really answer the question. It only equates when, say, the picture you've taken with a camera is blown up to be big enough to consume the viewer's entire visual field. At that size, the original photo would have needed to be approximately 576 Mp.
Detail for a picture is usually measured in DPI (dots per inch), and, even then, the size and distance from the viewer have to be fixed in order to determine how dense the dots have to be for the human eye to no longer be able to tell they are dots.
High quality print made for the average reading distance (18-24 in.) is on the order of 5-10K DPI. For a 1 inch square picture (@10K) that is 100 Mp right there ... for a 1x1 inch picture.
The problem is that even though a general scene may only need 576 Mp, when the eye actually focuses on a specific region, all of its acuity comes to bear on that region. Thus a 1x1 inch picture needs to be much higher density to "fool" the eye.
To make a picture big enough, and yet detailed enough to be focused in on, well, the number of MegaPixels is huge. That's why you see glasses being used. The screen is much closer to the eye, thus making the picture denser and yet appear larger.
Say you have a 5 MP camera. That's roughly 2,200 x 2,200 pixels. If the sensor (CCD) is roughly 1 in x 1 in, that is ... you guessed it 2,200 DPI.
Now blow that up to an 8 in x 8 in photo, and it is only 275 DPI. Nowhere near the 5000 DPI you need for a high quality print. (however, if you look at it from 8 times as far away ... )
To be honest, 2K DPI is passable for a standard print (@ reading distance), and when viewing a photo on a small screen (or print) it looks much more "real".
To get a 4x5 @ 5K DPI you'd need 500 Mp. @ 2K you still would need 80 Mp.
Roughly speaking, a 24 Mp (CCD) camera is equivalent to 35mm film quality.
Of course, there are a lot of enhancement techniques you can use to "fill in" the missing density when you have a digital image.
But if you need big pictures, old fashion film can be made in much larger sizes than CCDs can ( 8in X 10in film for example: http://answers.yahoo.com/question )/index?qid=20061123192628AANDiGx )