Chances are you have not specified a proper relative folder path for your image files or the background image file. Verify that the image file exists in the relative folder path you specified. Also remember your image files when you transfer your GED-GEN pages to your website at your Internet Service Provider (ISP).
When transferring your web pages to your website, remember to transfer the Cascading Style Sheet (CSS) file. GED-GEN automatically creates this file in your destination folder. It is usually named base.css, but will have the same file name prefix as the other pages (e.g., grpbase.css). If this file is missing, your family pages will appear without the colors, fonts, text positioning, and background image you specified.
Yes, the Multimedia Galleries feature will create gallery pages of the multimedia items referenced within your GEDCOM file. Gallery pages display small thumbnail images. Click on a thumbnail to display a slide page, which displays a larger view of the image. You can also link to the original image itself. In addition, you can display “primary” images as portraits for both individuals and family groups.