Wow, I wonder if this is the issue.
My site, a swedish one with no Amazon links tanked as well. Not even bringing in half the money it used to.
When searching site:domain.com every picture of my site is popping up. So you think this might be the issue? Have you recovered anything by using noindex on pictures again?
I can't be 100% positive this is the problem but it's one of those things that it doesn't hurt to get fixed anyways. Its the classic definition of thin content and we know Google does not like that.
What I don't get is that it happened Mid-March and why now in May do I see the effects overnight? Maybe Panda rolls around monthly?
Several of us did make the changes days ago but we did it to where it would redirect but I don't think that fixed it. The posts were always noindex for years so I did the noindex route today to see how it goes. The problem is that Google is slow to reindex so it could be days or even weeks before we see the changes. I do have one site that is showing promise as the results number dropped by 50 and the today's views to the site are a little higher but I can't give a for sure on it.
Even if this is not affecting our rankings something like this should have never happened and I'm wondering why Yoast allowed this to happen for months and not notice themselves or send out a patch.