Given that to be protected by copyright, a picture must be original/unique, I have read on the internet that the "product pictures" (of general use products like fridge, mobile phone etc.) are not considered as unique and thus are not under copyright. Is this true? Or do I need an approval from every producer?
If yes, at a first glance (just to see if it worths to spend more time about thinking of the idea & asking a lawyer) would this case be legal?:
The added value: the collecting (getting pictures from dozens of sources to one database) + the sorting/naming.
Remark: I don't want to collect the description texts! Only pictures.
I think you're confusing taking a photo of a product not being a violation of copyright with the copyright of photos someone has taken of a product.
If you have a refrigerator in your kitchen, and you take a photo of it and sell it, you're not violating the copyright of the refrigerator manufacturer on their design. It's a mass-produced consumer product -- not unique.
If you have a painting in your living room, and you take a photo of it (or scan it, or get out your water colors and paint a copy of it) and sell it, you are violating the painter's copyright. It's a unique original work (or even if it's a print, it's a licensed reproduction of a unique original work) that's protected by copyright.
Likewise, every photo on the web is a unique original work protected by copyright unless its been specifically released into the public domain or been given another license. If you make a copy of it and sell it, you're violating the photographer's copyright (or that of the company that purchased the copyright from the photographer).
Thus, I don't think your idea as proposed is legal. But I am not a lawyer, and this is not legal advice.
It all depends on what your doing and how you sell them. Fair use law might come into play.
http://www.copyright.gov/fls/fl102.html Good Article on the subject:
http://www.socialmediaexaminer.com/copyright-fair-use-and-how-it-works-for-online-images/ Depending on what you are doing perhaps stick with Creative Commons or just buy them from a royalty free stock photo company.