Google Chrome 67.0.3383.0 (Official Build) dev (64-bit)
Google_Samus.6300.276.0
Chrome OS with flag enabled: #enable-experimental-accessibility-features

# Enable STS
# Navigate to https://en.wikipedia.org/wiki/Echidna 
# Highlight area around picture of echidna, invoke feature
Expected: nothing read
Actual: file name read

You can also see examples of reading alt text at http://www.freedomscientific.com and looking at the Facebook, Twitter, etc. buttons. 

It's unclear if this is a bug or not so I'm filing nonetheless.