1) Many insects see through compound eyes which are made up of repeating units called ommatidia. The ommatidia take in light from their surroundings and transfer it to the brain. Inside the insects brain, the visual information is combined to form an image that allows the insect to make decisions based on its surroundings.
2) Based on their design, insects see a pixelated world. The more ommatidia, the more points (or pixels), the better the resolution. Dragonflies for example, require large numbers of ommatidia to catch their prey, and some species may have as many as 28, 000 ommatidia in each eye (source: http://sci.waikato.ac.nz).
3) Despite the multitude of ommitidia, the visual acuity of the compound eye is still about one hundred times less than that of the human eye. The only possible way an insect could see with as much detail as the human eye, would be to make their eyes 20 meters in diameter!
4) The compound eye is also good at detecting motion. As an object moves across the visual field, the ommatidia are progressively turned on and off. This on/off mechanism results in a "flicker effect" that allows insects to respond to moving objects. For example, a foraging honey bee is more likely to visit a wind-blown flower over a stationary flower.
4) Insects also process visible information differently than we do. The blowfly can process visual images more than four times faster than humans. That means the rapid scanning eyes of a blowfly watching a movie would simply see the image as separate frames, since the images are displayed at 25 frames/second.
Now, try imagining what the world would feel like if you could process information at that speed. Everything would look as if it were moving in slow motion. That's one of the reasons it's so difficult to catch a fly. Though I can do it, but only blindfolded with chopsticks. Po taught me. (;