Did you know that only 13 of the 50 states explicitly prohibit dressing room surveillance without the expressed permission of the shopper? If you aren't in Alabama, Arkansas, California, Delaware, Georgia, Hawaii, Kansas, Maine, Michigan, Minnesota, New Hampshire, South Dakota, or Utah, you should check up on your local laws.
In some states, it is perfectly legal to use one way mirrors, sometimes also referred to as two way mirrors, to spy on the customers. This in combination with cameras, which also happens to be legal in some states, means you've probably been caught exposed on a camera before.
Consequently, there is a fairly large chance, that a random stranger has watched you change before.
Now you also have to keep in mind, regardless of store policies and other possible regulations, data can definitely be stolen/ miss used... I'll leave the rest up to your imagination.