for example, i have a database with images files (.jpg for example), and i have another image (for example my gmail picture), i want to search images similar or "near" to my image

some points that i'm thinking about... images have many data, including meta data, maybe not only querying images (faces for example) but search a barcode or a ocr text, and many others features (i know some features when i worked with some opencv projects)

ideas and informations and experiences are wellcome :)
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