So, now knowing what copyright is and how to protect your images, lets talk about what you can do with those images.  For the most part, the images are yours to do whatever you want with in your portfolio, print as artwork for your home or grow your business.  The devil that is in the details comes when you want to try and sell them or submit them to magazines.    If the images are just of nature, wildlife or many inanimate objects you should be good to go. It gets more complex when the images contain people, architecture, some locations, and some famous locations (even objects that contain logos).  

The first question is "when would I need a model/property release?"  Model releases in general are used due to privacy, so depending on who or what is in the image, the answer would vary.   If you are shooting images of random people even in public places, models on a set, or anything depicting people for the most part for commercial usage, then sure you would need a model release.  For editorial images; editorial being images that are connected to an article and not an ad, then for the most part a model release would not be needed. ( editorial can include newspapers, educational books, trade magazines.)There is still gray area here in many cases. 

There is also moral and ethical ideals behind some of this.   Many years ago, you could shoot the backs of people  in an image and as long as their face was not showing and a release would not be required.  Today it is very different.  If a person can recognize themselves by the clothes, handbag, height, hair, watch or in anyway, then a release probably is going to cover you and keep you safe from legal issues later.  There have been several lawsuits in recent years where the persons face wasn't showing but they were able to distinguish themselves and filed a lawsuit against the photographer or company using the image.  So there are some that would interpret that using an image without a release, even though you cannot identify the person/s in the image, allows for moral/ethical interpretation whether or not it should be used in some cases.   This is why I hold to my practice of getting a model/property release in almost all scenarios.  It is only then that you have written documentation of consent from the subject in the image.

Again, I am not an attorney, but my opinion and practice has been to get a release almost every time I am shooting people.  I have even been so bold to ask for model releases from random people I have shot in public.

Here is a great article from asmp http://asmp.org/tutorials/property-and-model-releases.html

What about trademarks? 

What is a trademark: A trademark is a word, phrase, symbol or design, or a combination of words, phrases, symbols or designs, that identifies and distinguishes the source of the goods of one party from those of others. A service mark is the same as a trademark, except that it identifies and distinguishes the source of a service rather than a product. Throughout this booklet, the terms "trademark" and "mark" refer to both trademarks and service marks.  

Do Trademarks, Copyrights and Patents protect the same things?

No. Trademarks, copyrights and patents all differ. A copyright protects an original artistic or literary work; a patent protects an invention. For copyright information, go to http://www.copyright.gov . For patent information, go to  http://www.uspto.gov/main/patents.htm .

(source: http://www.uspto.gov/trademarks/basics/trade_defin.jsp)

So what if I shot a photo that has a trademark or logo in it?

Again it depends on what you are doing with the photo that will determine what you need to do. In general its similar that I can keep the logos in an image used for editorial/educational purposes.  For commercial usage, then the logo/trademark would have to disappear or not be present at all.  

A good scenario is that if I shoot down a street in a city I will capture all kinds of logos and trademarks.  If my subject is the street of the city, I am fine, but If my purpose was to somehow imply that one of those logos/trademarks is being represented or sponsoring that image, that's when I would get into trouble.  Then the interpretation comes in trying to decide what your intent was.

Keep in mind, the laws on the books are up for opinion and interpretation in a court setting, so FAIR use doctrines are only good until you sit in front of a jury or judge and a decision is made.  Fair use for logos/trademarks and copyright differ, its good to seek it out and read up on both.

Some good resources:

http://www.lawmart.com/forms/difference.htm

http://smallbusiness.chron.com/fair-use-logos-2152.html

http://copyright.lib.utexas.edu/imagguid.html

Fair use of digital images: http://www.copyright.gov/help/faq/faq-fairuse.html