CCDciel is free software released under the terms of the
GNU General Public License
Astrometry.net can be used to solve the image you just take with your camera. Astrometric solving will give the exact astronomical position of the image center, its orientation and size.
CCDciel requires a local copy of the Astrometry.net software including the indexes on your computer. It can also run Astrometry.net on a remote host using the provided script.
At page http://astrometry.net/use.html you can find detailed instructions how to install the software and indexes.
On Linux astrometry.net is probably packaged by your distribution. This is the easiest and preferred way to install the software.
For example on Debian or Ubuntu just do:
sudo apt-get install astrometry.net
Then to install some indexes:
sudo apt-get install astrometry-data-2mass-08-19 astrometry-data-2mass-07
For macOS the simpler option is to get the version from CloudMakers.
To use this version with CCDciel, first run it from it's interface to initialize the application correctly. Then you need to change the following in the CCDciel Preferences at the astrometry tab:
If you use another version of astrometry.net on your Mac you must be sure it can be called from CCDciel without specifying a path.
If you need to add the path you can modify one of the example script located in /Applications/CCDciel/scripts to suit your needs.
A number of Windows package include a fully automated install of Cygwin and astrometry.net and it is best to get one of them. CCDciel do not use this applications but the astrometry.net they install. Cygwin is a tool required to run a compiled version of Astrometry.net under Windows.
The following list indicate tested application and give the Cygwin path you must configure in the astrometry preferences.
At the time of writing all these application use the same 2010 version 0.38 of Astrometry.net.