From the comments on the article by the author it looks more like 10% so far and they haven't systematically looked. That means ~10% if a probable floor of how much fraud there is.
More like 10%, but my search has not been systematic. I am mostly looking where I know I will find image issues based on image filenames and “Find Similar Images” searches.
They are clearly saying they think this is likely above average.
Not according to the complete comment:
They are clearly saying they think this is likely above average.