When a listing has no images, GeoDirectory shows a fallback image instead. It checks these in order and uses the first one it finds:

1. the listing’s logo, if the post type has a Logo field and the listing has one
2. the Default Listing Image of the listing’s category, set under Places > Categories when you edit a category
3. the post type’s Default image, set under Places > Settings > General
4. the Listing default image for the whole site, set under GeoDirectory > Settings > Design > Archives

So for one placeholder across your whole directory, set the site-wide Listing default image. To vary it by category, set a Default Listing Image on each category.

Choose which fallbacks an image block uses

The GD > Post Images block has a “Fallback types” setting (fallback_types) that controls this list. If you don’t want the logo to be used as a stand-in for the listing photos, leave it out:

[gd_post_images types='post_images' fallback_types='cat_default,cpt_default,listing_default']

To show only the logo somewhere, such as in a header area, use [gd_post_images types='logo']. The “Image types” setting (types) picks which uploaded images show, and the logo is only mixed into the post images when you list both.

The fallback images are shared by the listing as a whole. A logo or other image field can’t have its own separate default image.

More settings for this block are in GD > Post Images.