There are 3 things you can do if your Snapchat keeps freezing when it gets to the pictures part:
1) Close the app, double click your home button (on iPhone) and swipe the app window upwards to dispose of it.
Once it's gone, reopen the app.
2) Make sure you have the latest version of Snapchat installed on your phone. Even if you are up to date, it still might be worth unintstalling and then reinstalling Snapchat.
3) File a report about this big at https://support.snapchat.com/
Why does my Snapchat freeze every time I take a picture?
The only other thing that comes to my mind is that it could be an issue with your memory. Have a look at how much storage space you have left on your phone, and if it is low you could try saving some of your photos or videos stored on your phone to another device or in the cloud.
You could also access the Snapchat app's log files if you are more technically minded and see if there is any information about bug reports crashing the app for example.
On an iPhone, you can go into Settings > General > About > Diagnostics & Usage > Diagnostics & Usage data
And then see if there are any reports titled "Snapchat"
That kind of data might be helpful if you are submitting a bug report to the Snapchat team.
