You have upload approval enabled. You need to approve the upload. Only CB Moderators are exempt from upload approval. Either turn off upload approval globally in CB > Configuration > Images, within the canvas field specifically in CB > Field Management > canvas, create a Joomla menu item to CBs image approval page and approve those uploads, of publish the CB Workflows module in Extensions > Modules as it has a link to the image approval page if there are pending approvals.
Is this your first time using CB? Was the site handed off to you from a developer? I strongly recommend you read through the CB Primer Book, which you can download below.
www.joomlapolis.com/downloads/documents
We also have a set of videos that walk you through CB configuration, which you can find below.
www.youtube.com/playlist?list=PLp0puRITgC7PuyzPsMUECDI46VE7IFSAX