The larger pictures you will have to upload to a photo site to host - most forums have a limit on the size of attachments to save on bandwidth.
I use www.fotopic.net for mine - most are free to register.
For the avatar - go to 'my controls' and then the avatar link, there is a limit for this also so you may need to reduce the size of the picture to fit. For this though you can upload direct from your poota.
Hope this helps.