I've had mixed success using www.onlineocr.net -- it's free and technically has a cap on how many images it can do per hour, but I've only hit that limit once, when trying a new method where I broke the OCR into dozens of smaller pictures.

In general, it does a passable job, but can be really hit-or-miss. Anything with marginal patterns or pictures in the background is a no-go, and like I hinted at in the beginning, longer pages tend to lower its accuracy. If the surface isn't glossy, it works much better on pictures taken using flash. I like to get a setup with an overhead light, a lamp, and natural light if possible and have 2/3+ light sources to help illuminate well and minimize shadows and glare.

When I say it can be hit or miss, I mean that it does a fine job 80% of the time, but sometimes it will get a text totally wrong -- as in, not a single legible word. This can be the case even when every other image from the set renders fine. But this isn't a very common issue and I think tends to be more likely if the image I'm trying to OCR isn't ideal.

As a side note, I've discovered recently that Google Drive auto-OCRs images and non-searchable text documents (ie scanned PDFs). This is great for finding things, but you have to format your stuff correctly. It will only tell you the document the word came up in, but not which page -- as a result, ever document I wanted searchable I broke up into single-page TIFFs or PDFs, and then I just have to read the one page rather than a large document.