The photo above is a close-up of a male horseshoe crabs compound eye. The females eye looks the same and both male and females have two located on eiether side of their shell.
If you look closely you can see the multiple lenses that make up their eye. There appears to be about 100 or so (I haven’t counted them). Each of the lenses sees a portion of an overall image made up of shadows in black and white.
Horseshoe crabs do not see in color. The compound eyes are used mainly in the location of a mate and the can determine if it is day or night.