Picasso is a free Open Source Library. You can download it from the official Picasso website.
As of the time of writing, this is how you can load the Picasso library into your app build.
Select File>Project Structure
Click on your app name under Modules in the left pane
Click on the Dependencies tab then click on the plus (+) top-right
Select Library dependency from the pop-up menu on the right
Select Picasso from the list. Press OK, then Apply and OK on the next window to close the Project Structure window
In the Project window on the left, click on build.gradle (the one in your app directory)
Look in the dependencies() method for the com.squareup:picasso line and edit it so that it looks like the following image
You should include .picasso so that the line looks like the one above
Press the Sync Project with Gradle files button (circled in yellow)
You’re now ready to use Picasso. Just import it like you would any other class.
I hope that you have found this tutorial helpful.