Photos are amazing. They can make people smile, cry, laugh and feel pretty much every other emotion. They can also carry a lot of information.
For example a picture of you in your school uniform tells me which school you go to, your age within 4 years, and what town you live in or near. If it has a landmark in the background that makes it even easier to pin down where you are.
Then there is the impact it might have on your online reputation - If you are being silly will your employer see it - or your future employer? If you send it to a stranger what are they going to do with it? Why do they want it? Think about all of this before you share an image of yourself
When you are sharing images of others you need to ask their permission. "Can I put this photo of you on...". If they are fine with it, great go ahead. If not then you just don't share it. They might not like what they look like in it, or might be worried about who might see it, or maybe just don't want to look silly - they don't really need a reason though - if they say no, you don't share it, no matter how funny it is.
If the image of a more "adult nature", other rules apply as well. Click here for more on this.