Take another look at the sentence:
Attached to the email, Charlotte sent her boyfriend Byron another photographic
self-portrait with eerie red eyes.
Attached to the email, a participle phrase, is describing Charlotte when its target should be self-portrait. When a modifier is next to a word it doesn't logically describe, it is misplaced.
To fix the problem, you should revise the sentence like this: Charlotte emailed her boyfriend Byron another photographic self-portrait with eerie red eyes.