This is a good point and I agree with you Sean but I need to ask you a question to clarify this. Is it your original picture? Did you make this image using photoshop and was the image you used to make it (assuming you needed one) also originally made by you. If the author doesn't give credit then there is no doubt it is plagiarism. If it is your original artwork that they posted and credited but didn't ask for permission I think it's fair to simply ask them to remove it. If someone asks me to remove something and I know it's not mine it will be the first thing I do. Do you think that's fair? We can try to be the bigger person in the situation. If the same person does it more than once after a polite warning, flag them, mute them and find any way necessary to remove them from your circle. Thanks for your thoughts.