Netpbm consists of code contributed by many authors.  In most of the

source code files, there is a copyright notice and license, telling

you what you may or may not do with the code.  All authors have granted

you the right to use and distribute their code without having to pay

them, as long as you meet some simple requirements.

Most of the components require you to include a copy of their

copyright notices and warranty disclaimers in any copies or

derivations you distribute.

Another restriction that some of the software has is that in order to

have permission to copy it (which includes writing anything derived

from it), you must distribute source code for your copy or derivation

and propagate the same restriction to people who would copy your

derivation.  In other words, the price the author wants for the use of

his proprietary work is your contribution to the free software cause.

One component prohibits you from selling it or using it in a

commercial way: hpcdtoppm.

Some components are contributed to the public domain.  

The copyrights on individual components of this package are detailed 

at appropriate places within the package.  A slightly out of date

summary of all the copyrights is in the file 'doc/copyright_summary'

in the Netpbm source tree.

As with most public open source software, no one really knows for sure

where the code came from.  It is possible that a contributor copied it

without license to do so.  That might mean any user of the code owes

someone royalties.  The Netpbm maintainer in particular has received

no warranties regarding any of the code in the package.  So consider

all the above to be modified by "to the best of the Netpbm

maintainer's knowledge."

Netpbm may practice valid patents, which would mean that you owe someone

royalties if you use the code.  This is a miniscule risk, though.

What is known about patents related to Netpbm is in the file

'doc/patent_summary' in the Netpbm source tree.