I add a Picture "GaussBonnet with Jpeg format to the following question but it does not work.
Can one help me to resolve this problem?
It is difficult to give some advice since it is not clear what went wrong. The OP has confirmed in the meantime that now the images are visible in the post. As you can see in the revision history, all I did was adding the missing "!".
If a picture is uploaded through the editor, the Stack Exchange software should take care of the correct syntax for the picture. Of course, it is possible that when editing the post something goes wrong. Solution is either to upload picture again or try to edit the post into correct syntax.
The same can be obtained by
![MathOveflow logo] : https://i.stack.imgur.com/B3C50.png
However, as already mentioned, probably the best strategy is to upload pictures through the editor and leave it up to the software that the correct syntax for inclusion of the pictures is used.
Some relevant links:
The picture used in the example is taken from: Mugs, Stickers And Shirts - Now With 100% More MathOverflow!.