Kevin,
Thank you for your reply. altimg is in the Mathematical Markup Language (MathML) Version 3.0 2nd Edition recommendations, and it is in the Mathematical Markup Language (MathML) Version 4.0 working draft but marked as not core MathML.
Does the epub 3 support only core functions?
https://www.w3.org/TR/MathML3/chapter2.html#fund.syntax
https://www.w3.org/TR/mathml4/