To post them in line ( viewable in the post ) they have to be hosted somewhere and you use the "img" tag on the reply page to insert the image address. You can upload them into your RC gallery and use their image tag to do this, or upload them to a site that allows hotlinking.
You can also just upload an image from your HD, using the attachment option on the reply page. This however restricts the size of the upload.
HTH