Provided you use the plain text editor in combination with the HTML one, you may encounter the situation where the latter does not display your image while your browser loaded with the page does so (this problem also occurs when relative addresses are used). Therefore, it proves helpful to load one browser window with your page and another with the editor. Thus you can easily view the changes you have made in your page by reloading the contents of the former (using the Refresh/Reload button of your browser) each time you save them in the editor.