Update TeachingHub.md, Documentation/teachinghub-qrcode.png files

TeachingHub.md

@@ -97,10 +97,12 @@ I recommend using your phone and an app there, as this is the most secure way. A
 <img src="Documentation/teachinghub-qrcode.png" width="300px">
 
 When you scan to your Authenticator App, it will automatically get the details (username, Secret) required to generate every 30 seconds a Time-based One Time  Password (TOTP). Like this:
-![](Documentation/teachinghub-authenticator)
+
+![](Documentation/teachinghub-authenticator.png)
 
 The combination of username, password and TOTP needs to be used to sign in:
-![](Documentation/teachinghublogin)
+
+![](Documentation/teachinghublogin.png)
 
 This sounds all really complicated, but I promise this will be easier from time to time. Don't forget that this for our all security and your contribution is appreciated! Thanks.