Do:

var isTrueSet = (myValue === 'true');

using the identity operator (===), which doesn't make any implicit type conversions when the compared variables have different types.

Don't:

You should probably be cautious about using these two methods for your specific needs:

var myBool = Boolean("false");  // == true

var myBool = !!"false";  // == true

Any string which isn't the empty string will evaluate to true by using them. Although they're the cleanest methods I can think of concerning to boolean conversion, I think they're not what you're looking for.

The jQuery constructor accepts a 2nd parameter called context which can be used to override the context of the selection.

jQuery("img", this);

Which is the same as using .find() like this:

jQuery(this).find("img");

If the imgs you desire are only direct descendants of the clicked element, you can also use .children():

jQuery(this).children("img");