If you use a passive rule to audit the program and pull the event you will be able to see that this is actually a Window Store Application. 

 Host Domain Name NetBIOS: <None>
 Event ID: B58A5320-531A-4982-97C8-4890D0699365
 Process Start Time: 133924401027807608
 Process End Time: 0
 Event Time: 133924401027807608
 Authorizing User SID: <None>
 Authorizing User Name: <None>
 Authorizing User Domain SID: <None>
 Authorizing User Domain Name: <None>
 Authorizing User Domain Name NetBios: <None>
 Client IPV4: <None>
 Client Name:  <None>
 UAC Triggered: false
 File Owner SID: S-1-5-18
 File Owner Name: SYSTEM
 File Owner Domain SID: S-1-5
 File Owner Domain Name: NT AUTHORITY
 File Owner Domain Name NetBIOS: NT AUTHORITY
 Parent Process Unique ID: <None>
 Parent Process File Name: c:\windows\system32\svchost.exe
 COM CLSID: <None>
 COM AppID: <None>
 COM Display Name: <None>
 Source URL: <None>
 Authorization Challenge: <None>
 Windows Store App Name: Microsoft.ScreenSketch
 Windows Store App Publisher: <None>
 Windows Store App Version: 11.2409.25.0
 Drive Type: Fixed Disk
 Challenge Response Status: <None>
 PowerShell Command: <None>
 Application Workstyle Description: Snipping Tool
 Application Workstyle Id: c1f136d6-28ee-453f-bd95-fda62815fcea
 Message Type: Prompt
 IE Zone Tag: <None>
 MD5: 58F68A28F43AE748DB4B6CEAEB7A29E9
 Host Local SID: S-1-5-21-2867306486-2659972164-3988425936
 Trusted Application Name: <None>
 Trusted Application Version: <None>
 Uninstall Action: <None>
 Rule Script File Name: <None>
 Rule Script Name: <None>
 Rule Script Version: <None>
 Rule Script Publisher: <None>
 Rule Script Rule Affected: false
 Rule Script Result: <None>
 Rule Script Output: <None>
 Rule Script Status: <None>
 Auth Methods: <None>
 IdP Authentication User Name: <None>
 Configuration ID: a8712607-e4ba-413c-9a72-9eff35733db4
 Configuration Revision Number: 9
 SHA256: 8986DEF745FD6B7B2D39A1C39B7FA2A7958E5375F377EF18E1B0BB7575B7D8FF
 User Request Management Id: <None>

So you need to create a rule to block the snipping tool using a Windows Store Application with a store package name as Microsoft.ScreenSketch