No, Mike, you do not have to Reply to add another picture.
Each post can now contain up to 3 pictures maximum.
I added the pic to your first post. To do it yourself (after posting originally)
Look at upper right corner of your original post, click Modify (should show that button for 24 hours after the post was made, will then disappear).
Under the reply box below the post, look for the Attachments + (which is above Attachment 1).
Click on the +.
Another line will appear under Attachment 1,,,,, Attachment 2.
Browse and enter the location of second picture.
Click Post Message.
:)
I added some pictures to help explain above instructions