Step 1 Go to Structure > Content Type.
Step 2 In Article row, click "manage fields" link.
Step 3 Create "Image" field with following settings:
Click save and set following properties:
Step 4 Go to "Manage display" tab > Default tab, set following properties:
Step 5 Go to "Manage display" tab > Teaser tab, set following properties:
Step 6 Click "Save" button.