To add an image I suggest you to follow this process:

1. Download a free image (no attribution)
2. Open Paint an resize the lenght of the image at 780 PIXELS
3. Go to steemimg.com and create your account
4. Upload your picture on steemimg.com
5. Click on the menu and select "Direct linking" or something like that. It's the second choice from the top
6. Copy it in the section of the upload image on the editor

That's it :)

To have a better editor, check out http://steemtools.com/. You'll find a lot of utilities :)

Hope that helps!