@Md. Rubiat Haque
Thank you for your detailed post!
Based off our Azure AD Connect sync: Attributes synchronized to Azure Active Directory documentation, the thumbnailphoto attribute is "synced only once from Azure AD to Exchange Online after which Exchange Online becomes source of authority for this attribute and any later changes can't be synced from on-premise". This also applies to SharePoint Online, Teams, and Skype for Business.
Solution:
Use the Set-UserPhoto cmdlet or Outlook on the web to change the user's photo. These methods enable you to upload a photo that's as large as 500 KB.
Use the Set-UserPhoto cmdlet (for admins):
1.Connect to Exchange Online by using remote PowerShell. For more info - Connect to Exchange Online PowerShell.
$Session = New-PSSession -ConfigurationName Microsoft.Exchange
-ConnectionUri https://outlook.office365.com/powershell-liveid/?proxyMethod=RPS
-Credential (Get-Credential) -Authentication Basic -AllowRedirection
Import-PSSession $Session -AllowClobber -WarningAction SilentlyContinue
-ErrorAction SilentlyContinue
Note
- To use the Set-UserPhoto cmdlet to its full size capabilities, you have to change the connection URI by appending ?proxyMethod=RPS to the ConnectionUri parameter.
For more info on the remediation steps - User photos aren't synced from the on-premises environment to Exchange Online in a hybrid deployment.
Related threads with alternate workarounds:
Azure AD Profile Pictures not updating in an Exchange Hybrid deployment
Azure AD user picture is not synced / updated from Office 365
If you have any other questions, please let me know.
Thank you for your time and patience throughout this issue.
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