The RadEditor control is designed to act as a normal text editor and restrict content into its size dimensions. Like in desktop text editors, if you have a long paragraph text, it will fall to new lines. Opened in a larger document, the same paragraph will appear with less lines of text. This is an expected behaviro for the text editors.
However, you can apply a custom style to handle that:
As for the image, the RadEditor does not provide such functionality. Although, you can generate image data from HTML with canvas element. You can read more about it in Drawing DOM objects into a canvas
Check out the Telerik Platform - the only platform that combines a rich set of UI tools with powerful cloud services to develop web, hybrid and native mobile apps.