add cropping factor for image edges

[geezacoleman]

a cropping factor (i.e. % of frame size) should be added as default with numpy array slicing so users can set areas to ignore. Particularly relevant for use under hooded sprayers to ignore the edges of the hood.

[SeemabAyub]

i am student of MS i have a request that can you recommend contributions as MS thesis and also access to your dataset