>> Then you could add the picture in your report that looks like your preprinted form.
>
>The problem is not to print or not the picture. The problem is how to merge the preformatted image (whole page) with my report form or with my destination output (file to fax)? In other words, I need a way to merge a background image (not just a picture) into my report form?

Just run the report twice, one for print and one for Fax. In the first run you just will print on preformated paper, the second will be Faxing and the picture will be there. The report output must be the same.