The african continent has it share of CTO as well, unfortunatly.
Some countries have issued stamps that hardly are collected mint. In order sell the rather useless stamps, and to avoid they are re-used for postal usage. They are cancelled CTO.
Most of them are easily recognised, as the title says : the obvious ones.
The list of CTO cancels is nearly endless...
luckily the 'obvious' ones are easy to regognise. At least if you have a couple of the same country or set, to compare.
A good way to recognise is that the CTO cancels mainly refer to the capital city.
Liberia -> Monrovia
or the name of the country is on the cancel (you won't see that on most postally used cancels)
Togo, Tanzania, Equatorial Guinea, ...
or 4 stamps can easily be put together, forming the complete cancel.
Almost all of those cancels are printed, and not 'stamped' as they usually do in postoffices.