Optical character recognition

Optical character recognition, usually abbreviated to OCR, involves computer systems designed to translate images of typewritten text (usually captured by a scanner) into machine-editable text--to translate pictures of characters into a standard encoding scheme representing them (ASCII or Unicode). OCR began as a field of research in artificial intelligence and machine vision; though academic research in the field continues, the focus on OCR has shifted to implementation of proven techniques.

Originally, the distinction between optical character recognition (using optical techniques such as mirrors and lenses) and digital character recognition (using scanners and computer algorithms) were considered separate fields. Since very few applications survive that use true optical techniques the OCR term has now been broadened to cover digital character recognition as well.

Early systems required "training" (essentially, the provision of known samples of each character) to read a specific font. Currently, though, "intelligent" systems that can recognize most fonts with a high degree of accuracy are now common. Some systems are even capable of reproducing formatted output that closely approximates the original scanned page including images, columns and other non-textual components.

The United States Postal Service has been using OCR machines to sort mail since 1965. Mail sorting plays a small role in OCR research; OCR systems need only read the postal code on each envelope. After the postal code has been read, a bar code with the same information can be printed on the envelope. To avoid interference with the human-readable address field which can be located anywhere on the letter, special ink is used that is clearly visible under UV light. This ink looks orange in normal lighting conditions. Envelopes marked with the machine readable bar code may then be processed; machine readable codes can be decoded more quickly than human readable letters and numbers.

While the accurate recognition of Latin-script typewritten text is now considered largely a solved problem, recognition of hand printing and handwriting in general, and printed versions of some other scripts--particularly those with a very large number of characters--are still the subject of research.