1. Got o Extend from the administrative toolbar and install the following Web Services modules: Serialization and RESTful Web Services:

2. Go to Structure and then to Views. Click on Add view. Name the view API Users and make it show Users.
3. Check the Provide a REST export checkbox, and type in the api/users path. This is where requests will be made:

4. Click on Save and edit.
5. Change the format of the row plugin from Entity to Fields instead so that we can control the specific output.
6. Ensure that your view has the following user entity fields: Name, Email, and Picture.
7. Change the User: Name field to a plain text formatter and do not link it to the user, so the response does not contain any HTML.
8. Change the User: Picture field to use URL to image formatter so that only a URL is returned and not HTML.
9. Save your view.
10. Access your view by visiting /api/users; you will receive a JSON response containing the user information:

[
  {
    "name": "spuvest",
    "mail": "spuvest@example.com",
    "user_picture": "\/sites\/default\/files\/pictures\/2017-07\/generateImage_xIQkfx.jpg"
  },
  {
    "name": "crepathuslus",
    "mail": "crepathuslus@example.com",
    "user_picture": "\/sites\/default\/files\/pictures\/2017-07\/generateImage_eauTko.gif"
  },
  {
    "name": "veradabufrup",
    "mail": "veradabufrup@example.com",
    "user_picture": "\/sites\/default\/files\/pictures\/2017-07\/generateImage_HsEjKW.png"
  }
]