I did not find information on the API on the imagecms website.
Globally, there are two ways to do this:
1. OneBox crawls into the ImageCMS database. Such a solution, since we cannot give any guarantees. Something will change - the integration will break.
To make such a revision is 16-20 hours.
2. Ask ImageCMS developers to make an integration so that ImageCMS transfers data to the regular OneBox API.
The developers are officially ready to do this
https://www.imagecms.net/services and this integration will not break because the OneBox API does not change.