Make sure you use relative links for your inserted images. The original picture and this page were stored in two separate folders. I inserted the image into a Composer file, and then saved the file, but not the image. However, when I saved the file, Composer saved both the html file and the picture into the same folder, without asking me about it. Here is Composer's image properties window:

Check the image properties. The picture is identified with just its file name: no drive, directory, URL, or folder. It is a relative file, and the browser looks for it in the same folder as the page into which it was inserted.