There are two ways to post pictures.
You can store them online somewhere then insert the url where they are using the "insert image" button above ( the second from the left in the lower row). There is a maximum size, but I forgot what it is. I don't post larger than 460x480. When you click the button, you get the start and end of the image line. Bring up your picture with your browser, copy the url for it and paste it in the middle where your cursur is. That will put a full picture in like this:
The other way, which is my choice as a rule, is to upload it directly from your computer as an attachment. That gives you a thumbnail in the post that will give a full version of the picture when clicked on. This is good because it doesn't take all day for pards with dial-up to load the thread. They have the option of viewing the thumbnail or the full picture if they like. That is done by clicking on the "Additional Options" on the left just below the text window where you are writing your text. You can type in the location of the photo or browse your computer for it. The maximum size is 128K and you can only do two per post. That way the photo looks like this: