Yes. If commenting was enabled on the project you can comment without being logged in to Picter. To stay in the loop of the conversation you need to leave your email address in the process. This address will only be used to inform you about comments to that project.
To leave a comment select “Comments” from the top menu. On the right, a sidebar appears. At the bottom of the sidebar you can enter your comments. In the comments sidebar you also find any comments that other collaborators might have written.
Comments are visible to anyone who has access to the project.