When you reply, on the icon bar just above where you enter is an icon that looks like a picture.
Click on that icon and a window will pop up. Click on From Computer and another will show. Click Choose File and a finder window will open. Find the image you want to load and select it, then click on the "Choose" at the bottom of the finder window. You will see in the place where you reply an html code to attach a file with a number between the html flags. That's your loaded image. Now if you just click Post Quick Reply, you'll post the picture. If you want to see it first, then click "Go Advanced" and a preview of the post will be visible to you.
BTW, If you are trying to post the popup windows, that's of no use to us. It doesn't matter what popup you want to block. What we are trying to get to is the App store to install a blocker that will block ALL popups. From the names in the post where you listed your own system locations it looks like that's what you are trying to do, at least by the filenames.