Something about copyright

i have some pictures which is not taken by me.
may i upload them to DH?

How to understand copyright infringement?
If something even i do not know if they are copyright protected, how should i deal with them?

And, if DH found a copyright infringement, will they disable this account immediately without any warning?

Who owns the photos?
What purpose do you want to use them for?
Why not get permission from the owner???
Curious !!!