User blog comment:Kirkburn/Technical Update: May 29, 2017/@comment-24014422-20170530090633/@comment-126761-20170530140207

It's just a tweak in the way it checks PNG files for errors, to avoid some situations where valid files were being rejected. This does not affect the maximum filesize (10MB) or resolution (12.5 megapixels) - though we are separately considering increasing the latter.