When posting/editing a post, click on Go Advanced. It will come up with a separate page that gives you more options. Find an icon of a little Paperclip called 'Attachments'. Click that, and it will bring a small popup that allows you to upload (up to 5 at a time) files. Once you've uploaded your screenshots, their filenames will appear in the popup. Right-click them, and open them in a new tab. This will open the image up. Then right-click the image, and select 'Copy Image Location'. Close the pop-up window, return to your post, and there will be an icon of this