No need to get cynical. I use my php_manual.chm frequently, but never seen isset been used like that.

As I see it, line 2 in the above code reads as one of the following 2 options:
PHP Code
false and $Picture = $user['USER_AVATAR'];
or
PHP Code
true and $Picture = $user['USER_AVATAR'];

This only makes sense if php uses a construct called "complete boolean evaluation". I know this construct from basic, but I've never seen it be used in php.

But hey, maybe php does indeed behave the same and break an evaluation as soon as an "and" clause hits a "false" condition.
Still, even if that's the case, I wonder why you would write your code like that. If you code it like in line 3, it requires only 1 character more, but it would be a proper "if" clause which will never fail. Not even if the syntax rules in a next php version be changed to not break an evaluation upon the first "false".

Just my 2 cents.