Encoding for W3C Validation

Hello List.

In the Alt section of the IMG tag below, the variable $myitem has a value of "Who's There".

echo "<div class='myclass'><a href='#' class='color_thumb'> <img src='/itemimages/$mypic' alt='$myitem' width='60' ....

When running through W3C validator, the line errors out because of the " ' " in "Who's".
I tried:
$myitem=(htmlentities($myitem));

But this has no affect on "Who's".

What's the best way to code this portion so the apostrophe is handled correctly?


TIA,

--Rick