It may so happen during posting in our blogs, we require relevant images which we search from Google Image Search. I always try to visit the website where the image appears and try to find out any copyright info. If I don't find anything in the website, I try to see in image properties. If no copyright info at all, how should I use the images? Or, should I avoid using images from Google Image Search? Or, will it be helpful if I mention 'copyright info unknown' / 'copyright belongs to photographer'?
Every single picture has a copyright. You can't be sure that a website is automatically the holder of the copyright. Beaware of landscape or product images. There a people making money with copyright lawsuits. For example: I heard about someone who add's images of food to the internet and he makes 1000 EUR of every single copyright offense.
Oh God! This is also a way to make money for some people? They add images and later sues people for using them?
When people think it's OK to use the copyright of others without permission then that's what happens. What this person is doing may sound immoral at first reading, but he isn't doing anything to encourage people except to upload images that he owns. It's just the greed of people who steal his images without permission that he pursues, and he makes a healthy income from it, it seems. Don't blame the owner of the copyright, blame those who attempt to steal his images. That probably answers your original question too. If you don't have the copyright owners permission to use the images then you could be on shaky ground.
You always pay more for a copyright breach than you would have to pay to get permission before using it. All images are copyrighted and so you must look for those that explicitly state they aren't (ie the owner has waived their rights) and so if there is no comment on copyright you assume you cannot use them. Depending on what sort of images you are looking for you are better off either using one of the stock image sites which offer royalty free images. There are one or two that are free but most charge around $1 for a small image and then you at least know there won't be a $2000 bill to follow
I am not blaming anyone, not telling someone is doing immoral things. Since I don't want anybody's right to be violated, that is why I asked "If no copyright info at all, how should I use the images? Or, should I avoid using images from Google Image Search? Or, will it be helpful if I mention 'copyright info unknown' / 'copyright belongs to photographer'?" But to me, the situation looks like majority of Internet users (almost 100% of us) have violated others' copyrights - knowingly or unknowingly. I feel a little better since I don't want to do this anymore and so I raised the questions above. Lastly I feel, I must start using my own images or stop using images inside my web articles I am ready, but how many else are?
It's a pretty basic concept - If something isn't yours, you need express permission to use it. While many people do steal pictures, it certainly isn't anywhere near "100% of us".