The following assumes you are in the United States. It is also general in nature and should not be taken as legal advice. The particulars of your situation could be different than the general situation outlined in the question, and any one such peculiarity that might seem relatively minor to you could swing your entre case in a different direction. You need to consult an attorney who specializes in intellectual property and personality/privacy concerns in your jurisdiction.
Do I need their consent or even a model release if I:
- want to upload the picture to my portfolio
- want to exhibit the picture somewhere
- want to sell the picture
You own the copyright to the photos you take, absent an agreement/contract/terms of employment that states you have assigned those rights to others. Copyright, however, does not necessarily give carte blanche to use those images in any way one wishes. Copyright protects you from other entities using the images you own without your permission. There are a wide variety of factors that affect just how one may use an image they own.
- Where the image was taken. If you were on public property when the photos were taken, you are allowed much wider usage absent the permission of others than if you were on private property. In the latter case you might need the consent of the property owner(s) and the consent of the photographed, who may or may not have had an expectation of privacy at the time. Since it sounds like you got permission to shoot from an authorized individual representing the university and the person photographed was aware you were photographing them at the time, the individual pictured in the photo probably has no grounds to contend an expectation of privacy at the time the image was taken. But that only means you were good to take the photo. It doesn't give you unlimited usage rights.
- Who and what is recognizable in the image. If the individual can not be identified, either by the contents of the image or by a description of the image, the individual probably does not have grounds for a claim that you appropriated their likeness or name. This isn't always as clear cut as it may seem, though. Just because a face is not visible or clear enough to be recognizable does not necessarily mean an individual is not recognizable.
Just for sake of example, let's say the individual was an employee of the university from the janitorial department who wears the same uniform every day and is the employee primarily responsible for cleaning that specific building. If others familiar with the university, that building, who cleans it, and the uniform they wear were to see the photo, they can reasonably be expected to recognize that a specific person is being depicted, even if their face is not visible. "Hey, that's the embryology lab in building 403, so that must be Bill who wears that uniform every day when he cleans it." You might even have used someone else who is similar in build and skin tone to "Bill", who wore clothing made to look like "Bill's" uniform, and created a space that looks like the place where "Bill" normally works. You're still possibly appropriating "Bill's" likeness. If your stand-in for "Bill" is depicted in a negative light (as defined by "Bill" and supported by what a reasonable person would consider to be negatively impacting "Bill's" reputation or character), "Bill" might have cause to sue you for libel or defamation of character!
- The type of consent your model gave (or didn't give) you with regards to usage rights. Some types of usage require no permission at all. Editorial usage, for instance. If you had permission to be there by the property owners and the individual(s) in an image had no reasonable expectation of privacy, you're probably clear to use the image editorially. Editorial usage can be included in a commercial publication, such as a newspaper, magazine, or publicly accessible website as long as the function of the image is to present or support editorial content. You're also fairly clear to use such an image for artistic or aesthetic use. This would include exhibiting the photo somewhere for its aesthetic value, or selling prints of the photo, or perhaps a photo book that contained many images, so that others could enjoy the aesthetic value of the image. On the other hand, commercial usage generally requires the permission of any identifiable person in an image. Commercial usage, by and large, implies the pictured individual(s) support and endorse a product or service (or perhaps an ideological position or political candidate) that the image is being used to promote.
Since you've been intentionally vague about the actual contents of the image, it's hard to answer your three sub-questions more specifically. Is there any nudity involved? Anything else that might be considered embarrassing or defaming? Anything that implies a certain type of character or specific belief or ideological position with which the unrecognizable person might disagree? All of these things must be considered before editorial or artistic usage can be considered.
- Portfolio usage is generally considered to be editorial in nature as long as images are not presented in such a way that those pictured are implied to have recommended your services as a photographer.
- Exhibiting a photo for its aesthetic value is generally considered artistic usage. If an image is one of several displayed on a wall with a banner at the top advertising your photographic services, however, you're probably now into commercial usage.
- Selling prints or digital copies of an image for the personal use of the buyers is generally not considered commercial usage. Just because money changes hands does not automatically make the use of an image commercial. The determining factor for commercial usage is whether or not the person(s) in the image are seen to be endorsing something. Newspapers sell editorial content every day (or at least they used to before the internet started giving it away). Prints or digital image files are sold for their aesthetic value all of the time.
Just because you are not required to obtain permission and waivers from an individual you have photographed for certain types of usage does not mean it isn't a good idea to, when possible, get such agreements in writing anyway. Most commercial portrait studios have language included in their standard order form that all customers must sign before being photographed that gives the studio particular rights to the images produced and indicates that the customer acknowledges that they are aware that they are granting such rights to the studio. Such a written agreement helps protect the studio if the customer ever changes their mind and decides after the fact that they regret having the photos taken.