Karen, You can either post the photo in your gallery. Or, when you click on reply, you can "click here to choose your attachements" link. This is the window that opens when you click on choose your attachments.
Current upload number is 1 . Maximum number of uploads is 9 . Step 1. Click on 'Browse...' button to choose your attachment file. (maximum size allowed = 300 KBytes , max width = 1200 px , max height = 1200 px)
Step 2. Define your attachment type:
Step 3. Click on 'Upload File!' button to finish. The uploaded file name will automatically be added to the attachment textbox. Close this window
When you add the image/images as attachments to your message you are limited to a small file size vs when you upload them to your gallery.