Here's how to manually add an image in the Editor.
Go to the content box.
*You cannot do this with the "Image" content box.
Open the source.
You should now see the HTML editor. Copy and paste the HTML provided below into the HTML editior.
<p><img alt="Mountain View" src="http://www.photosdaily.com/wp-content/uploads/2012/12/Happy-Cat.jpg" style="width:540px;height:350px;" /></p>
Now select the image link embedded in the HTML.
Copy/paste the link for the image you want in the old link's place.
*Be sure to use an image with high resolution for the best results.
You can now change the width and height of the image manually if you want. The width cannot go beyond 540 pixels.
Be sure to keep the ratio of the image in mind.
Click Save and Done at the bottom left of the content box and your image should appear.
If the image size is not to your liking you can continue to adjust the width and height in the source HTML.