XF 1.3 Tapatalk thread images missing

Cheers to all. First of all i am sure this is not a bug i may just overview a configuration setting.

Anyway i am looking for to use the thread images in Tapatalk. I've seen this on many board and they looks good.

So when you check the thread list some thread has images usually 3 of them.

On our board this is not working. We're not using attachments. All images are linked from external sites.
I thought this is the reason, but i've seen some sites that the IMG inserted external images also appear this way.

Any idea what i should look at to turn this on or off later if i am not happy with?

Thanks for your help guys in advance.