Hit & miss
The Telegraph published a chart of the figures for URLs reported for having illegal content.
Out of 50,587 public reports only 9,133 were confirmed as possibly illegal.
Out of 23,352 pro-actively processed 22,133 were confirmed as possibly illegal.
The chart legend actually says says "confirmed as child sexual abuse imagery". Given some of the historical cases where even juries have decided otherwise - then it is a moot point exactly what IWS had "confirmed". They have a vested interest in boosting their figures.
They seem to be saying that much of the material is hosted on "by invitation only" pages in general picture sites. It makes one wonder just how much they are immersing themselves in the trade in order to establish their credibility to access such invitations.
The very high number of "public" reports of apparently innocent material suggests there are a lot of people who see "abuse" everywhere. Unfortunately they are often also vociferous in lobbying politicians and the media for disproportionately draconian measures.