Once the dialog window opens, click down on the right on GO ADVANCED
Then Scroll down, and click on MANAGE ATTACHMENTS
A window pops up, with a choice to add 5 images. (On my pics it says DURCHSUCHEN because the pc/settings are in German, but in English it will be something like ADD or FIND image.
Then once 1, or 5 images have been uploaded, click close Box, (to close the pop-up) and either PREVIEW, or SUBMIT REPLY!