As a noun crop refers to the produce of a cultivated plant or piece of land. Harvest has a very similar meaning. Both can be used figuratively.
Crop has other meanings - a very short hairstyle and it is also the name of part of a bird's digestive system.
As a verb harvest means to reap/gather. Crop as a verb means to cut short and can be used about photos, hair, grass etc. Animals such as sheep are sometimes said to 'crop' a field and in this case it means to bite off.
I've got one more question,
verb discriminate should always be used with against? e.g. They are discriminated against their colour of skin. My ex-boss used to discriminate me (against) and got away with it? Are there any cases in which against is not required?