The default answer is no you cant.
It doesnt matter whether the image is of faces buildings or anything else. Heres how it basically works.
When someone presses the shutter on a camera the image formed is copyright to that person. Just the image mind you. By default every piece of artistic creation is copyright. The person holding the rights to an image can put it up on their own website and they still retain those copy rights.
However, some people often disclaim their copyright and then the image goes into the public domain and is free to use by anyone for any purpose for no fee. You can search for a public domain photo of green carpet and your good to go. Often the image will be tagged as public domain or CC0.
A person who holds the copy rights may at their discretion offer a license. The license terms can be anything they want and its up to you whether you want to accept them or not. If theres an argument about the terms then it ends up in court and it costs money on both sides. To prevent that argument being done over and over for a zillion different wordings of license terms some sensible group came up with the idea of standardizing a set of license formats which have been well chewed over by lawyers so that they ought to stand up in court. There are many of these but a set called Creative Commons is a group of licenses. The license may say that you can use the image but only for non commercial projects. Or it may say you can use it commercially but you must credit the copyright holder when you do. Sometimes it says you can modify the image and sometimes its whats called ND or non derivative.
If you get a license that is CC-BY-SA for example thats creative commons, credit the copyright holder and also that you must include the statement that any derivative work is also tagged with the same license. In this way you can use the photo of green carpet and sell it in a product but you must mention the original author and also all items that you sell that use the carpet texture must also be allowed to be used by other people in a CC-BY-SA way.
If you want my opinion then either get hold of definitely public domain images or ones marked as CC0 which is to say they are public domain. Or take the photo yourself and save the hassle of looking.
Now if you take a photo of peoples faces for commercial reasons then you may need to get their permission and statement saying you could. If they are in a public place with no expectation of privacy then your normally ok to do it but most journalists etc would ask if its not a public figure.
If you take a photo that contains other peoples artwork then you may be in breech of copyright. This has extended to cars, buildings and basically anything that has some design element to it. You may also have trouble with trademark issues if you copy and promote an image which contains a trademark if there is any likelihood that there would possibly be any confusion as to who is selling the item.
So yeah, nightmare. My opinion is to use only images that have a definite license statement your prepared to stick with or take all your own photos and draw your own stuff.
Specifically for textures you ought to be able to find public domain textures. You can use google images and set the usage rights to narrow down the search pretty well. Lots of websites offer up public domain images such as Pixabay - https://pixabay.com
See also: WikiCommons - https://commons.wikimedia.org/wiki/Main_Page
Click on any of their images and it comes up with a load of blurb. Somewhere in it will be the license. For example todays image has this:
Code:
I, the copyright holder of this work, hereby publish it under the following license:
Creative Commons attribution share alike
This file is licensed under the Creative Commons Attribution-Share Alike 3.0 Unported license.
You are free:
to share – to copy, distribute and transmit the work
to remix – to adapt the work
Under the following conditions:
attribution – You must attribute the work in the manner specified by the author or licensor (but not in any way that suggests that they endorse you or your use of the work).
share alike – If you alter, transform, or build upon this work, you may distribute the resulting work only under the same or similar license to this one.
Which means you could take it, modify it, but whatever derivative you publish using it has to have the same license. So you could print it on a T shirt and even sell the T shirt but you would have to make it clear that the image came from that author and its CC-BY-SA licensed. Someone else could take the image from your T shirt and make another derivative of it and sell that too with the same conditions.