The photos are the property of your parents, not you. They can use the photos as they see fit (with some limitations such as child porn, defamation etc) and do not need your permission.
No different to celebrities who sometimes have unflattering photographs appearing in trashy magazines.
There are likely to be future events more challenging in your life than having photos shown to friends. Rather than becoming indignant or upset, use this as a growing exercise so you become more resilient and stronger as a person. What they do is their choice, but how you react is your choice.