compare images from database

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i m making a fish smart app in which i am trying to compare two images.The images for comparision are stored in local database.The image of any fish will be clicked by fisherman using camera and then be compared with the images from database.If two fish images matches then its okay otherwise the new image will be added to the database. the problem is that many fish spicies have almost same shape,size,texture etc which makes it really hard to compare. not sure how to start with.Does opencv provides solution to this problem? any suggestion or link will be appreciated.