The forum area accepts uploads of standard image files such as GIF, JPEG/JPG and PNG. However it is important to understand that there are file size and dimension restrictions. You might also find that it doesn't like long file name or names with lots of spaces in.

When you compose your post, move the cursor down to the area below the text box area that says "Select Image file to attach". When you move the mouse down to this area, take a note of the message that appears in yellow above the text box area. It is information that is designed to help you.

Take a look at the example below. Here the cursor is down the bottom, but the area just above the text box is indicating the maximum file size (in this case 180K) and the maximum dimensions (600x900) that you can upload...

Once you click on the button to choose your file, select the image you want to upload off your Mac, as you can see in the example below...

If you haven't followed the size and dimension restrictions you're likely to receive warning such as the one below. You are going to need change the image before it will be accepted for uploading.