Did you know that when you post an image to Facebook, you are giving non-exclusive rights to Facebook to use the image as they please. Same applies to Twitter and Instagram. To understand what this means, we need to examine copyright.
When you create a work, as for example a painting, sculpture, novel, piece of software, etc, you automatically have copyright to it. That includes photos you have taken or images you have created. The only exceptions are where you are under a constraint such as that which may be applied by your employer or client.
Copyright gives you exclusive rights the moment it is acquired. You can assign these rights or some aspect of them to other parties. For example, you could give one publisher local territorial rights and another international rights. You could also place limits on how long those assigned rights will last.
The rights assigned can be exclusive or non-exclusive. If the latter, you can continue to exercise them for your own benefit.
Facebook requires you to give it non-exclusive rights to images and other IP content that you upload. This is what it says:
For content that is covered by intellectual property rights, like photos and videos (IP content), you specifically give us the following permission, subject to your privacy and application settings: you grant us a non-exclusive, transferable, sub-licensable, royalty-free, worldwide license to use any IP content that you post on or in connection with Facebook (IP License). This IP License ends when you delete your IP content or your account unless your content has been shared with others, and they have not deleted it.
So you get no royalties. Note that term sub-licensable. That means they can transfer the licence to another company, and without your permission. I find that a very one-sided deal, especially as, like most people, I don’t read all the small text. I just assume good faith. However…
Not at the moment. Whether Facebook, given its current exposure to regulatory inquiry, will soften its stance on this and similar issues, remains to be seen. If you don’t want your photos being used elsewhere by Facebook, I’d suggest deleting them. However…
You could make your images unattractive, not only to Facebook but to all those who believe that anything on the web can be copied for their own purposes. One way is to apply a watermark, which is what I do for some of my own material. You can also lower the picture quality: keep the size small and drop the DPI (dots per inch). It will look grainy if used at a larger size, making it unsuitable for posters.