How do I get my photos to display in full screen?

[iMore Question]

My photos are displaying in reduced size. How do I get to full screen.
Was full screen two days ago

 

[Just_Me_D]

1. What device are you using?
2. What app are you using to display the photos?
3. If it's an iPhone, have you tried rebooting the phone?
4. Were the photos taken in portrait or landscape mode?