Build/Get-DockerImageForBuild.ps1

function Get-DockerImageForBuild {
    Param(
        [Parameter(Mandatory=$true)]
        $TeamProject,
        [Parameter(Mandatory=$true)]
        $BuildID
    )

    $BuildDetails = Invoke-TFSAPI ('{0}{1}/_apis/build/builds/{2}' -f (Get-TFSCollectionURL), $TeamProject, $BuildID)
    $EnvJson = Invoke-TFSAPI ('{0}{1}/_apis/git/repositories/{2}/items?path=environment.json' -f (Get-TFSCollectionURL), $TeamProject, $BuildDetails.repository.id)
    $EnvJson.image
}

Export-ModuleMember -Function Get-DockerImageForBuild