There are a few programs that can scan music. SharpEye (Windows only IIRC) is a commercial program that does it. There's also a free program Audiveris (Windows/Linux). There are probably others, but these are two I have.

I've used SharpEye occasionally (I don't often have the need to scan music to score) and Audiveris I found just recently and haven't done more than a few test scans with it. They can both output MusicXML, which can be imported into score programs which will play it for you.

Like text OCR the scanning is not usually perfect and the programs include editing facilities to correct the initial reading of the score. For a simple tune it may be quicker just to type it into a score program and have that play it for you.

Mick