how to upload a picture into an edited post?
 

Is it possible to upload a picture without using the "upload picture" feature which is only available when you create a new post?

The easiest way is to upload to a site and link to the image using the [img]XXXXXXXXXXXXXXXXXXXX.JPG or BMP or GIF[/img] command.

Actually, I figured out another way....

START a new (dummy) thread to use the upload feature, but don't submit it. I think the picture gets uploaded to Pelican before the thread is completed, and then you can copy the image location into the old post.

Correct. You can do the same thing in the thread that has the post you're editing with "Post Reply."

Other way is to cut and paste the old information from your post to a new post with the photo, then delete the first post entirely. You can thus modify your post without it showing that any editing was done but it will have the new time stamp.