Set up a table of records with one record for each brand. Define a field that identifies the Brand. Define a container field into which you can insert the brand image. If you already have record with one table per brand, you can add the container field to that table.
Link this new table to your layout's table by the Brand Identifier. Put the container field from this table on your layout. When you enter/or select a brand identifier the associated image will appear on your layout.
Thanks Phil! I think I should be able to do that. I've been tearing my hair out... :-)