FilePickerExternalImageSearchEnabled is set to
true, which is the default setting, then any time a content editor is using the modern interface to choose an image, for example, in a "hero" webpart, or simply "image" webpart, they are presented with a dialog that allows the user to choose from "Recent" images, perform a "Web search" for images, look in "OneDrive" for existing images, look in the current "Site", "Upload" a new file from their hard drive, or paste in a "Link" to an existing image. See the following screenshot of the Image Picker with the "Web Search" option selected.
When this setting is set to
set-spotenant -FilePickerExternalImageSearchEnabled $false, the "Web Search" option is no longer visible in this commonly used Image Picker dialog. See the image screenshot below.
Note, that like most tenant-level settings, it can take 5 minutes or more before each site in the tenant picks up the new setting. Also, to see the new value with
get-spoTenant immediately after the change, you would need to either start a new PowerShell session or execute
disconnect-sponline and then re-connect.