I recommend Photoscape. It's free, fast and versatile. Resize your pictures with the longer side at 800 pixels. Save them as .jpeg images at less than 180KB size. (You will be able to adjust the size when you 'Save As...') Upload the image(s) using the Manage Attachments function. This is available whenever you compose a reply to a post. (However, this is not available when using Quick Reply.) Have fun