Hello Sir, I read your project's description, and see the site example you give. I can make you the pin generator application in c# if you don't care about the language, because it's better fitted than C language for doing this type of task.
Based on the sample pins you posted, I could make you similar template, and like pingenerator website, the application will generate the pin and you would be able to post the pin to pintertest, or to schedule the pin as needed.
We could discuss more in chat about the exact features you want for your app.
Thanks you very much for your attention.