Both can act as nouns and both can act as verbs
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.
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