You can specify within your profile on the forum whether you are open to constructive criticism of your photos. This will show up whenever you post, clearly indicating your preference to other forum members.
You set this up by editing your profile (Profile/Edit Profile/Personal). If a member elects to not want constructive criticism of their photos, we ask that everyone respect that. This is a friendly forum and we want to keep it that way.
As noted in our forum rules, we prohibit any forum member from editing the work of another forum member without obtaining permission of the original poster. You must obtain that permission directly - a user who states a preference for wanting constructive criticism of their photos must still expressly give permission to another member to edit their photo.