From my point of view, you should assemble your portfolio with the audience in mind. For example, if you’re freelancing, your portfolio should reflect the work you’re trying to get. If you’re looking for employment, build your portfolio to cater to the type of employer you want.
With that in mind, working within pre-existing branding standards is common. So is working with other people’s photographs or implementing things clients want instead of what you might personally recommend.
In some ways, graphic designers are like movie directors or symphony conductors. We think things through, we weigh the options, we consider what we have (and don’t have) to work with, then we coordinate it to achieve the best possible results under the circumstances. Like a movie director, we don’t necessarily write the script, do all the acting, or argue too much with the producers who have lined up the funding. Like an orchestra conductor, we don’t play all the instruments, write the music, or handle the ticket sales.
Graphic designers are not jacks of all trades who do everything on every job. We work with others who contribute (or interfere) with the job. Designers solve problems within the parameters of what we have to work with. We’re not simply people who make things look pretty — we take what we have to work with and are often expected to turn a sow’s ear into a silk purse.
Your portfolio is your opportunity to communicate to clients and art directors that you understand this and know how to work with others to obtain the best possible results. A portfolio isn’t about showing what’s only 100% yours. It’s about showing how you managed to work with the things available to you and how you achieved results.
For example, if your portfolio is online, your accompanying text should explain what you achieved and how you accomplished it within the problem’s parameters, such as budgets, collaborators, client-supplied photos, deadlines, etc. If you show your portfolio in person, it’s a chance to explain how resourceful you are to the interviewers.
In movies, directors always put their names up front in the opening credits. However, at the film’s end, another set of lengthy credits lists all the hundreds of things the director didn’t do and entrusted to others.