Modify Blog content type

Step 1 Go to Structure > Content Type.

Step 2 In Blog entry row, click "manage fields" link > Add "Image" field with following settings:

Step 3 Click "Save" > "Save field settings" button > Set following properties:

Step 4 Click "Save settings" button

Step 5 Go to "Manage display" tab > Default tab, set following properties:

Step 6 Go to "Manage display" tab > Teaser tab, set following properties:

Step 7 Click "Save" button.