Commenter is referring to the binary data at the beginning of the file, which makes up the file header for the jpeg. It is before the <html> tag and is neither commented out or actually ignored.
The browser actually picks that "text" up and shows it on page. It's just the html content itself contains some css rule to make that text not visible.
Edit: Misread your comment...the bytes at the beginning of the file are hidden by CSS (as pointed out by others).