Ahh I know what you are talking about now.

If you are in the forums and you are typing in a message and you click the button to insert an image from the gallery from the editors tool bar, you are not actually accessing any part of the Gallery module.

It just happens to be what the developers of the ftbeditor happen to call the button.  It defaults to the root folder of the portal so you shouldn't expect to see photos that are in the Gallery module unless you drill down to it. 

Any issues about how that works for subportals would probably be answered best in a more general forum or from the ftbeditor development site forums.

So this raises the questions:

How do I access my gallery images and display them in a forum posting?

If I'm regular user, can I quickly upload an image to the gallery while entering a thread and show an image in the thread?

From what I can see (I don't use this feature much) you should be able to add any file that is in the file system under the portal root but none of the folders under that.  So in other words unless you have permissions to write to the portal root you wouldn't be able to upload a photo there.

All of that is if you are using the FTBeditor button.

If you have the Gallery module loaded and the Forums set up with Gallery integration and also allow file uploads you will end up with two new buttons below the editor.  Use these buttons to insert photos into your thread and upload smilies.  When you click the insert picture button a new window opens and you can upload your photos then select the one you want to insert.