We suggest the following workaround.
In your Business Rule that sends the operation for approval insert the Run a program or PowerShell script action before the Send this operation for approval action and paste the following script:
$thumbnailPhotoBytes = $Context.GetModifiedPropertyValue("thumbnailPhoto")
# Convert the photo to Base 64
$thumbnailPhotoBase64 = [System.Convert]::ToBase64String($thumbnailPhotoBytes)
$to = "firstname.lastname@example.org" # TODO: modify me
$subject = "My Subject"
$bodyText = $NULL
$bodyHtml = @"
The image of user %name% (%username%) will be changed to:<br />
<img src='data:image/jpg;base64,$thumbnailPhotoBase64' alt='User image'>
$Context.SendMail($to, $subject, $bodyText, $bodyHtml)
The script will send the modified picture to the email address specified in the $to variable.
So, if you specify a manager's email in the script, he will actually receive 2 emails: one containing the image and sent by the script, and another one sent by the Send this operation for approval action.