Thanks for your tips.
Perhaps i explained myself badly, i''m sorry.
I don't want to open a random picture with gallery. I want an app to open the SAME picture every time i open the app.
Imagine that you have a picture of your grandmother on your wallet, i want more or less the same thing on my phone
I just need press the app icon and voilá, my picture is shown in fullscreen. that's what i was looking for.
Yesterday i was watching some videos on youtube and i now have more or less the idea what i need to do to make such an app.
The problem is that i'm not very savvy with with Java and Android SDK and it will take me some time create the app that i need.