There are two things you need to do in order to delete/remove/unsnyc Picasa album photos from your Gallery app.
1: Unsync Picasa Photos from your gmail so no more photos will populate on your S5 Gallery app.
2: Remove existing Picasa photos from your Gallery Photos app.
Other Cool Galaxy S5 Video—–
How to Screen Mirror Galaxy S3/S4/S5 Wirelessly:
Here is my personal review as a full time user between the Iphone 6 & Galaxy S5:
Here is my Galaxy S5 in under 8 feet of salt water while snorkeling in Bangkok:
Galaxy S5 vs Xperia Z3 Personal Review / Full Time User & Water Test: