Remember, unlike other software programs, Composer does not actually insert the image data into the HTML file. You have to have the original GIF or JPG file and the HTML file in order for your document to read properly. This saves room on your disk and shortens download times for documents. I strongly recommend, that you scale the images to their desired size in a graphics program before you insert them into your HTML document. Play with these settings, and preview them in your browser's window to guague their effect.
Alternate text is displayed while an image is loading and in text-only browsers.
Alternate text is not always necessary for each image, but it can be useful, particularly with the pop-up feature in newer web browsers, or if images take a long time to load. Low resolution images are a relatively new feature of Composer. It requires you to specify a second file that's displayed while the larger image is loading. These images are not supported by all browsers, and are not very common in current web design.