This is a brief explanation of how to add pics to a post. Any time you want to add pics to a post you have to use the full editor. The full editor is automatically used when you start a new thread, but when you reply to an existing post, the quick editor is used. So, if you want to add pics to your post, you have to change to the full editor. Look at the bottom of your reply. You will see the three buttons in the first attached pic. Select Full Editor.
When you are using the full editor, you will see a link to the attachment manager in the lower left hand area of the screen. (The second attached pic.)
Click on Attachment Manager. That will bring up the attachment manager. (The third attached photo. You will notice that, at the bottom of the photo, the first two pics are listed.)
Edited by PM, May 10, 2023: Khansen added this information for us. Very helpful:The screen shots that Paul posted work, but for the computer-challenged among us, here's a screen capture video I put together for posting photos with captions. Just follow the pointer. POSTING A PICTURE WITH A CAPTION [flickr.com] Before you move the image over into the box, you must add the caption for the image. The video shows this! It's easier than you think. 
Click on Select a File to Attach. This will bring up the file manager for your operating system and allow you to locate and select the file. (The fourth attached pic.) You will notice that the Choose button is greyed out. That's because I had not yet selected a file to attach. You MUST select a file and click on Choose at this point, or no pic will be attached.) Please note: the popup window on your computer may appear differently than this one, and the button may not say Choose. It might say Select, or something similar. This depends entirely on what OS you are using. I use a Mac.
Once you've selected the file, you may notice a rotating circle in between Select A File To Attach and Done. That is an indicator that the file is still being uploaded. Do not do anything until that goes away.
Once the file is uploaded, click on Done. When you do that, you should see the file or files you've uploaded listed below. (See the fifth pic.)
You should notice several things. 1) The pic are attached in the order that you attached them. 2) There is a trash can on the right side of the list pic that allows you to delete the pic. 3) The attached pics have the names that you gave them. 4) The total number of attached files is listed above the file list as is the maximum number of files you can attach. (There is also a cumulative size limit, so you may not be able to attach ten files.) 5) Files are limited to 500 MB, but the software reduces their size to save space on the server.
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Edited by PM, May 10, 2023: In case you slip by this in the middle of this post.
Khansen added this information for us. Very helpful:The screen shots that Paul posted work, but for the computer-challenged among us, here's a screen capture video I put together for posting photos with captions. Just follow the pointer. POSTING A PICTURE WITH A CAPTION [flickr.com] Before you move the image over into the box, you must add the caption for the image. The video shows this! It's easier than you think. 