Members of an FC are allowed to take the items (or in this case credits) that are offered to them for that purpose. Taking stuff that's been offered that way could only be regarded as stealing in the most extreme of cases (generally involving wiping out everything you can get and leaving nothing for anyone else, which if it was accurately described isn't the case here). Simply taking a picture from your FCs credits that's designed to be gotten by using your FCs credits certainly falls under allowable use.