When you hit reply, you scroll down to the "Attach Files" section. From there you click on the button "Manage Attachments" and then "Upload Files From Your Computer." Be sure your photo is in JPG format (there are other formats, but JPG is the most popular) and is less than 5 megabytes (you can find this by right-clicking on the photo and selecting "Properties). Click the "Browse" button and find the photo on your computer. Once you have selected it, click the "Upload" button in the upper right corner. It will then upload and attach itself to your post. Hope this helps.