The following procedure should work for posting .jpg files:
1. at the bottom of the screen when you open up a new reply thread there is a statement "Attachments and other options". Click on that.
2. It will open up additional items including "Attach". click on the "choose file" button
3. You will get a default-selected folder opening up with a list of disk drive items at left margin. If the default did not include the illustration you want to post, select the drive from the list at the left and scroll down to the item you want to post. In this case, I selected the photo hj4.jpg.
4. if you have other photos, click on "(more attachments)" . You will get a new "choose file" that you can click on. In this case, I selected the photo p1010039.jpg.
5. If you have additional photos to post, repeat step four. You can post up to 6 attachments onto the actual posting item. If you selected the wrong file just click on "(clear attachment)" at the item you want to replace. When you are done attaching items, at the lower right corner of the screen there is a button marked "preview". You will see your text with a section showing the illustrations that should be posted with the text in your reply.
6. "Post" button should put everything up. I did this to get the posting with illustrations of a 1952 Henry J dashboard and the display board front side that Barbara created to help show off our 1952 Henry J Corsair deLuxe.
7. I added this item to show off the "Modifiy" selection at the upper right area of the text box. Clicking on this lets you add text, illustrations or delete illustrations as well as delete areas of the text you posted. I used the modifiy function to add this after verifying that what I wanted posted came out ok.