javascript - How to get the children of the $(this) selector?

You can find all img element of parent div like below

$(this).find('img') or $(this).children('img')

If you want specific img element you can write like this

$(this).children('img:nth(n)')  
// where n is the child place in parent list start from 0 onwards

Your div contain only one img element. So for this below is right

 $(this).find("img").attr("alt")
                  OR
  $(this).children("img").attr("alt")

But if your div contain more img element like below

then you can't use upper code to find alt value of second img element. So you can try this:

 $(this).find("img:last-child").attr("alt")
                   OR
 $(this).children("img:last-child").attr("alt")

This example shows a general idea that how you can find actual object within parent object.
You can use classes to differentiate your child object. That is easy and fun. i.e.

You can do this as below :

 $(this).find(".first").attr("alt")

and more specific as:

 $(this).find("img.first").attr("alt")

You can use find or children as above code. For more visit Children http://api.jquery.com/children/ and Find http://api.jquery.com/find/.
See example http://jsfiddle.net/lalitjs/Nx8a6/