I'm trying to set up an HP C4280 to send a scanned image to the Pi disk when the "scan" button on the scanner is pressed. HP expects a Windows program to be running, but I'd like to be able to scan to a file and retrieve the file later. Has anybody done something similar? I don't know where to get hold of the api for the HP scanner.
Have you tried the HPLip package? It is on raspbian repository.
Features supports and info for your model: http://hplipopensource.com/hplip-web/models/photosmart/photosmart_c4200_series.html
It's unlikely that you're going to "get ahold" of the api. Printers don't have a public API; you need to get the driver directly from the manufacturer. HP doesn't offer a Linux driver for the C4280, let alone a drive compiled for
Alternatively, you could try and reverse engineer it. This would be a monumental task and is unlikely to work well on such a complicated device.