Unable to build apk due to cannot find symbol picasso.fit();

That's an issue with the version 1.20 of the plugin.

You can use 1.1.18 and it works well with that.

Here is how to move to 1.1.18

$ ionic cordova plugin rm com-sarriaroman-photoviewer
$ ionic cordova plugin add [email protected]

Build and it will work

cordova build android 

...
...
...
:app:transformResourcesWithMergeJavaResForDebug
:app:packageDebug
:app:assembleDebug
:app:cdvBuildDebug

BUILD SUCCESSFUL in 32s
46 actionable tasks: 46 executed

If this still gives you the same error as earlier, try removing the android platform once and adding it again,

$ cordova platform rm android

$ cordova platform add android