ImageObject not recognized by Google for BlogPosting

Hello,
We use Enfold’s schema markup-helper on our blog. We are getting the following errors for our blog posts in Google’s Structured Data Testing Tool:

The property ImageObject is not recognized by Google for an object of type BlogPosting.
A value for the image field is required.

And a warning:
The image field is recommended. Please provide a value if available.

I saw some previous threads for this issue. However, I was unable to follow the solution as it was provided over several forum posts. Could you please provide a solution for this problem? Thanks!