Upload the pics to your computer. When you start a thread or even reply there is a section the says manage attachments. Click that and upload the pictures. You may want to use
Image hosting, free photo sharing & video sharing at Photobucket also. On photobucket you can resize the picture so it is not to big when people click on the thumbnail to see it. If you use photobucket you can copy the website link onto a reply. Hope that helps.