run this on one of your ddcs. It should spit out the vm or snapshot used for the image. Just replace the $CatName variable with yours
asnp cirtix*
$CatName = "W10NDJMCS"
$Cat=Get-brokerCatalog -Name $CatName
$ProvScheemUId = $Cat.ProvisioningSchemeId
$ProvScheme = Get-provScheme -ProvisioningSchemeUid $ProvScheemUId
$ProvSchemeName = $ProvScheme.ProvisioningSchemeName
$Image = $ProvScheme.MasterImageVM
Write-host $Image