The idea of an API-driven OCR service came up at last month's iDigBio Augmenting OCR Hackathon.
I wasn't involved in the team that built it, as I got distracted detecting handwritten sources from OCR output, so I'm afraid I don't know very much about how far they got. Nevertheless, I'd recommend taking a look at the documentations for the REST API they developed: https://github.com/idigbio-aocr/RESTAPI/tree/master/doc Ben Brumfield http://manuscripttranscription.blogspot.com/
