How do you identify reducing / non-reducing sugar by looking at structure?

Identifying reducing / non-reducing sugar been confusing me for a while now , I know that reducing sugar contain aldehyde or ketone group . It's easy to identify them in monosaccharides but this becomes confusing in case of disaccharides! 
![enter image description here](https://i.stack.imgur.com/FoVM1.png)


I fail to see carbonyl group here, How can I identify reducing / non-reducing sugar by looking at structure in picture? can anyone help me out?




Many sugars are drawn in the cyclic, closed form where the carbonyl group has been converted to a [hemiacetal](http://en.wikipedia.org/wiki/Hemiacetal). 


![enter image description here](https://i.stack.imgur.com/OFpF5.png)


Once you realize that a hemiacetal can equilibrate with a carbonyl (*e.g*. it is a carbonyl in disguise), identification of reducing sugars becomes easier.


Here is an example from [Wikipedia](http://en.wikipedia.org/wiki/Reducing_sugar), it is Maltose, the same as your third compound


![enter image description here](https://i.stack.imgur.com/Yk9w0.png)


See the aldehyde in the open isomer drawn on the right; see how it can close to form a hemiacetal on the left.


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