Here is a small PowerShell script to fix the pictureurl for all userprofiles after changing the mySite Url:

$mySiteWebapplicationUrl = ""
#current Url of your mySite website

$mySiteOldUrlValue = "http://mysitetest:80/"
#former Url where your pictures do not reside any more

$mySiteNewUrlValue = ""
#current Url where your images can be found now

$mySite = Get-SPSite $mySiteWebapplicationUrl
$SPServiceContext = Get-SPServiceContext $mySite
$userProfileManager = New-Object Microsoft.Office.Server.UserProfiles.UserProfileManager($SPServiceContext)
$userProfiles = $userProfileManager.GetEnumerator()

foreach ($userProfile in $userProfiles)
  #if pictureurl is not empty replace the old url part with the new one
  if ($userProfile["PictureURL"] -ne '')
    $oldPictureUrl = $userProfile["PictureURL"].toString()
    $newPictureUrl = $oldPictureUrl -Replace $mySiteOldUrlValue, $mySiteNewUrlValue
    write-host "oldPictureUrl = " $oldPictureUrl " --> newPictureUrl = " $newPictureUrl
    $userProfile["PictureURL"].Value = $newPictureUrl