Can I control that thumbnail on the photo album box in the timeline page of the profile? This box appears besides the "Friends" and "Likes" in a default profile schema.
That box displays the photo you were most recently tagged in. To control the photo, just upload a new picture (or select one in which you are not already tagged in) and tag yourself in it. Whenever you're tagged in a newer photo, you'd have to redo this process to maintain a persistent image on your profile.