There are two different ways to add a image to your message, using a image URL or upload a image from your computer.

Using Image URL

1. Click on flow icon;

2. Choose a pre existing flow or create a new one;
3. Add an Action Set, and click on the attach icon on the bottom right;

4. Click on attach URL;

5. Click on Image on the drop-down menu;

6. You can insert the image URL, after that you can call the image using the variable @extra.attachment_url.

Upload an Image from your computer

1. Click on flow icon;

2. Choose a pre existing flow or create a new one;
3. Add a Action Set, and click on the attach icon on the bottom right;

4. Click on attach file;

5. Choose the file from your computer.