Thumbnail Generation Configuration
When it indexes a file and extracts information, Voyager creates a thumbnail and a preview for that file and stores them in the meta folder in your Voyager directory.
To configure how Voyager generates thumbnails:
Go to Manage Voyager > Discovery >  Discovery Configuration > Default SettingsÂ
Select the Thumbnails tab
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There are five Strategies for generating thumbnails:
Use Default Image StrategyGenerates images with default settings for the type of content being indexed. This process is dependent on the type of content being indexed.
Do Not Build ImagesThis allows the fastest indexing, since no thumbnails are generated.
Skip Preview Images Voyager creates generates a thumbnail and a larger preview image during indexing. This option prevents preview images from being generated and is faster than the default.
Build All Images at Index TimeThis option builds thumbnails for all results and is generally the slowest option.
Fetch Images from Web ServiceThis option fetches images from an external web service on demand during search. This option is faster than the default setting and uses less storage since no images are generated locally.
Render Images from GeometryThis option generates images by rendering spatial data from documents during indexing. This is generally the slowest of all the thumbnail options. See the "Best Practices when Rendering Thumbnails from Geometry" articles for configuration information on generating thumbnails from feature geometry.