Detect "red x" placeholders for images in Word 2011

I discovered recently that a Word 2011 doc with multiple (that is 100s of) images had some images that had been replaced with Red X placeholders. I had to chase a copy from backup to restore them. I was lucky this time and I was able to restore them.:)

So I tried to write a "red x detector" to run periodically to verify that all images were OK, but I wasn't able to figure out a way to determine that a shape is actually a red x placeholder.:(

My question: in VBA for Word 2011 how can I determine that a shape is a red x placeholder?

Thanks!