SharinPix can be integrated into Salesforce Classic in different ways.

For instance, it is possible to integrate SharinPix into your own Visualforce development or add the same on your page layouts.

Here are the possibilities you have : 

• Using SharinPix "Album" Canvas App
• Using Visualforce page Without A Controller (Admin Friendly)
• Using VIsualforce page With a Controller (Developer skills required)

The above links point to detailed instructions on how to configure each experience.

Best Practice is to use the Visualforce page integration.

If you want more flexibility, you should use the version with a Controller but, this requires some developer skills.