The apos entity is an XML built it, and isn't defined for HTML. While some browsers support it in text/html documents, this is error correction and you should not use it.
<img src='$IMAGE1' alt='$DESCRIPTION1'>
I can be sure that $IMAGE1
won't mess up my HTML formatting if I can ensure it doesn't have apostrophes, but otherwise it's impossible.
Are you aware of any browsers that don't support this entity in HTML?