Upload and resize your pictures onto your computer. Then go to a site like www.photobucket.com,
and upload them there. Once it's uploaded, it'll give you a URL link. It'll look something like: http://www.photobucket.com/anaronnismom'sfile/picture1.com.
You just put [img] [/img] around the link (the http:...com part inbetween the two img. brackets) and the picture'll show up when you post it.