If you are writing your own font recognition software and you plan to use a technique that you know is patented you could talk to the patent owner. The USPTO has a recordation office you can use to try to see if the patent has been assigned. Also on Google patents there is a link that takes you to the recordation database. If it is not in the assignment records you can contact the inventors. Looking up the patent in Public PAIR (lots of info in other answers) and looking at some the first filed paperwork (ADS, Declarations) should get you contact info. If PAIR shows an attorney or agent was involved they can probably get you in touch with the inventors or assignee.
A patent owner can refuse to license or can request/negotiate any deal they and you agree to. You might be able to get a field-of-use exclusive for your particular case. That would not only keep you kosher but make it harder for others who come along later to copy you - if the patent is that critical.
However if you are getting the software commercially, the vendor of that software should warrant that it either does not infringe anything or that they have licensed all rights needed. Also they might indemnify you.
Do you already know of a specific patent that might be at issue? Have you got qualified advice dissecting what the claims do and don't cover? Unless it is clear that you will be stepping on something, most people would just go for it.