One of the reasons it’s important not to post anything online that you wouldn’t want your grandma to see, is because nothing that you post or send online is ever truly private. Online posts and pics, and texts can be saved, passed to others, and used in ways that you cannot control (such as memes). Since your pictures are now online, your options are limited, but there are still steps you can take.
First, notify any social media platform where you see your pictures, and let them know that the images should be taken down and banned. Most social media platforms have a reporting system you can use to help at least reduce the spread of your photos on that particular platform.
Second, you can also let the person who is sharing your photos know that you are reporting their actions, so that they can work with you to take down the photos, knowing that their online access/social media access is at risk otherwise.
Third, talk to your parents, or if you truly can’t go to them, talk to a trusted adult about what is happening with your photos. If your photos are being spread everywhere already, chances are your parents may find out about it, and it may be best to go to them first, explaining that you screwed up and that you are trying to problem-solve. Chances are they may take away your online privileges, but that they will also help you put an end to the photos being spread.
Finally, take the lessons that you’ve learned from this experience as character-building, and also give yourself an internet/social media break. Taking a break can protect you from online shaming, seeing negative comments, and allow things to blow over. Ultimately your actions online need to respect who you are and others. In the future, post only those items that you are OK with being seen by strangers or your grandma, which is a part of being a thoughtful and responsible member of society in the digital age.