Slideshows can display custom thumbnails in the visual navigation area that are distinct from main image displayed on the slide.
Slideshows display the Original image preview in the visual navigation by default.
By customizing one of the other image previews, and then selecting this image in the Release settings, this can be changed using the following process.
Adding custom thumbnails to a slideshow
Navigate to the Media item's Image Preview editor in the Platform interface:
Media > 'Your Media Item' > Files
Then add the custom image you want use in the slideshow visual navigation area as one of the Image Previews by clicking the blue Edit icon at the top right of the preview image.
Then navigate to the Release that includes the slideshow to be modified:
Releases > 'Your Release' > Content
Find the slideshow to be modified in the list of elements in the Release - it will display the Slideshow icon to the left of it - and then click on the Settings icon.
The settings window will open to the right. Navigate to the Thumbnail Image Source dropdown menu and open it.
The dropdown will display options for each of the Image Preview options. Select the one you've customized.
After selecting the custom thumbnail source from the dropdown menu, make sure to click Save.
Click the Preview button to verify the change displays as expected.
Hovering over any of the items in the visual navigation will display the customized thumbnail.
The changes to any already published releases will be made only after republishing the Release.
To publish, click Releases > 'Your Release' > Publishing > Publish Button