That looks like you are using the Gravatar module, you could disable that module and in the Users > Users > Images tab replace the default image... You may want to do the same on the Profiles > Profiles > Images tab as well.
If you are not using the "Site Ads" you can hide that image by checking the "Hide Ads" checkbox in your ACP > Skins > YOURSKIN > Global Config > Site Ads tab.