Why can't I open pictures in my texts?

I have the new iPhone 5 and my friends and I send a lot of pictures. It worked fine, but maybe two days ago it stayed acting up. When I click the thumbnail in our conversation, it says loading and the top labels it as "img_(number).jpg". The only way I can see the picture is by saving it to my camera roll. Why is this happening and how can I change it?

I would advise you to just go to the closest phone shop. They will fix this for your easily without to charge you.

Reboot your phone. That fixed it for me.