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I post all of my images that I want to put in the Grumble to a storage website that my ISP provides for me for free. Most servers will do this for their customers. You will need to use an FTP program such as CuteFTP, BulletProofFTP, or WS_FTP to transfer them from your hard drive to your storage area.
When you post a message with an image you simply click on the "IMAGE" button under the text box where you enter your message and copy/paste or manually enter the URL of your image (from the storage area) and it will show up in your post.
Most people lack the FTP program but you can download one from this site or go to any of the FTP program sites and download a trial version of their program to try it out.