[Plugin: Simple Flickr Photostream] Horizontal display of thumbnails

The way the thumbnails are displayed is really down to your css so everything is possible really.

But the plugin does not include any stylesheet for you so you’ll have to do it manually.

Generally a simple li.picture-item {float:left;} should do.

Have a look in the comments on this page: https://www.ai-development.com/wordpress-plugins/simple-flickr-photostream-widget

There are a few ideas on how to display thumbnails in rows of two for example.