Image Not display

Hi

I would like to insert the image on the excerpt page, no matter how I set, the image is not display :

[display-posts image_size=thumbnail]

css code:

.listing-item {
clear: both;
}

.display-posts-listing img {
float: left;
margin: 0 10px 10px 0;
}

Still no image shown on the page. Is there anybody knows how to set this?

Thanks

https://www.ads-software.com/plugins/display-posts-shortcode/