External image 
You may have a field in the database that has the URL to an image, and you want to display that in Avo. That is where the ExternalImage field comes in to help.
It will take that value, insert it into an image_tag, and display it on the Index and Show views.
ruby
field :logo, as: :external_imageOptions 
-> width
-> height
-> radius
-> link_to_resource
 Wraps the content into an anchor that links to the resource. 
Use computed values 
Another common scenario is to use a value from your database and create a new URL using a computed value.
ruby
field :logo, as: :external_image do |model|
  "//logo.clearbit.com/#{URI.parse(model.url).host}?size=180"
rescue
  nil
endUse in the Grid cover position 
Another common place you could use it is in the grid :cover position.
ruby
cover :logo, as: :external_image, link_to_resource: true do |model|
  "//logo.clearbit.com/#{URI.parse(model.url).host}?size=180"
rescue
  nil
end
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