Welcome to Android Central! Picasa represents your Google+ Photos in the cloud that are syncing with the stock Gallery app. If you want to keep them in your Google+ Photo albums, but don't want them in the stock Gallery, then go to Settings>Accounts-Google>[your Google account], and uncheck Picasa. (On some devices, it's listed as Gallery.)
Now go to Settings>Apps>All, select Gallery, and Clear Cache/Clear Data, then Force Stop. When you open Gallery again, wait a few seconds for the database to rebuild. The Picasa photos should be gone.
10-28-2014 08:17 PM