There are two ways to add a manufacturer logo to the product listing page:
The logo/image can be inserted into the product description. This is done on the Products > Product List page. Click Edit next to the product, then enter the logo into the product's description field.
You can also insert the dynamic tag directly into the product listing template itself. The tag for this is [manufacturer_logo]. The product listing template can be accessed in the Settings > Design > Template Editor section or via FTP. You will need to write the path to the image so that it will look like this:
Be sure that each of your products has a manufacturer assigned to them. Otherwise, the image will display as a broken link.