If you have an iPhone, email the pictures as attachments to yourself. When you press send, the phone will ask what size you want the files to be. Choose small or medium. I guess there is a way for Andriod to resize also , I just don't know what it is. You will get the same prompt about size if you send a picture via email from an iPad to an iPhone and vis versa.
After resizing, same attachments as files and use those files for you post to the forum