I agree with Attorneys Burdick and Butterman and will go even further: There is NO risk that the incidental appearance of some company's trademark in your adult-themed photographs will cause consumers to falsely believe that the brand owner is affiliated with, sponsors, or endorses you or the photographs. There is NO infringement.
The brand owner's second argument is that the presence of its mark in an adult-themed photograph will "tarnish" the favorable associations that consumers have with the mark. So, the argument goes, consumers will think less of Coke whenever a Coke can appears in the background of a photograph if a naked lady appears center frame. The syllogism is patently silly: a photograph of a naked lady is "bad" so if a Coke can appears in that photograph then Coke must also be "bad."
There is NO empirical evidence that consumers make any such connection between the substantive content in art and marks shown incidentally but brand owners in their childish fits of self-righteous "brand protection" efforts go all group-think in the head and so sue and sue and sue whenever their marks are used in ways they don't control.
In short, the law permits incidental use of marks in art. But you'll be sued anyway.
The above is general information ONLY and is not legal advice, does not form an attorney-client relationship, and should NOT be relied upon to take or refrain from taking any action. I am not your attorney. You should seek the advice of competent counsel before taking any action related to your inquiry.
If your photos can be construed as being endorsed by or affiliated with the products, or your photo's subject matter causes an unflattering association with their brand, then you could expose yourself to a suit for trademark infringement, trademark disparagement, and trademark dilution.
You can understand why a well-known brand like Pepsi wouldn't want their product anywhere near anything sexually themed. They've spent a ton of money to establish their brand in the marketplace, and they obviously wouldn't want it tainted. Your photos may be very classy and high-end, but I wouldn't expect a TM owner to see it that way. I'd avoid including any recognizable TMed product in your photos.
I'd also consult an IP lawyer to make sure you're not treading on anyone's IP rights, and to make sure you copyright your photos when they're done, perhaps as a series.
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In the abstract, an incidental appearance of a branded item in the background (out-of-focus, partially obscured, etc.) may not be a problem, but if the "incidental" appearance is more prominent such that the commercial use of the picture could be construed as being endorsed by or affiliated with the branded products, then there could be an trademark infringement or dilution issue. This is not a question that can be answered in the abstract, except in general terms. Indeed, the devil is in the details. It would be prudent to have a trademark attorney review the photographs to determine what, if any, issues it may raise.
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If the appearance of the products is, as you say, truely incidental, it is legal. Also, there are few consumers who could be confused into thinking most of those brands sponsor, endorse or are associated in any way with XXX films. However, the fact that you ask tells me there is more to this than just that. For example, some of the things that would surely get you sued:
1. Having a porn queen using a Coke bottle and then saying "That's The Real Thing".
2. Having kinky sex scene on a MacBook laptop and saying "Think Different!"
3. Putting a Superman "Diamond S Shield" logo labeled "Super Stud" on a porn star.
You can see why a brand does not want those images.
The safest thing is to not do this, as the threshold for major brands to object is much lower for porn and judges and juries are not very sympathetic.
So far, this is free to you. Until you pay a fee, I am not your lawyer and you are not my client, so you take any free advice at your sole risk. I am licensed in IL, MO, TX and am a Reg. Pat. Atty. so advice in any other jurisdiction is general advice and should be confirmed with an attorney licensed in that jurisdiction.
All of the above advice is great and spot-on but I know from experience that using any well-known brand in association with porn is asking for trouble and at least a cease & desist letter should be expected. Companies with signficant branding programs are particularly sensitive to the tarnishment of their brands through association with porn and highly aggressive in trying to stop that association whether or not incidental or "legal" and justified in asserting such claims. You can claim the use is incidental or not a focus of the shot (what would be that is not the naked actor or actress?) but the bottom line is that you likely will have to invest time and money arguing this with Pepsi or Apple or whatever other brand is used and you should ask yourself if that is really worth it and budgeted in your photography. However much you budget, it likely won't be greater than the budget of the company whose brand you use.
Alex Butterman is a trademark attorney with Staas& Halsey LLP (http://www.staasandhalsey.com), a Washington, D.C. IP boutique law firm. Alex is admitted to the bars of Washington, D.C., New York and New Jersey but, unless otherwise specified, the answer is intended to be general enough to apply to any U.S. state and based primarily upon his knowledge and experience with applicable federal laws. The opinions expressed are those of the author and do not necessarily reflect the views of his firm, Avvo or other attorneys. This answer is for general information purposes only and is not intended to be and should not be taken as legal advice. No attoreny-client relationship or obligations are established herein, although consulting an attorney to discuss your specific situation is strongly recommended. This is especially true of trademark law and probably any area of intellectual property law because TM law is so fact-specific and full of esoteric nuances and exceptions, that more often than not there does seem to be harm in handling a trademark matter without consulting an experienced trademark attorney.
Let's be practical. Incidental use of a brand in a manner that does not cause consumer confusion is perfectly legal most of the time. But sometimes even incidental use may have a tendency to tarnish the reputation of the brand, resulting in "trademark dilution". Most famous brand owners do not want to be associated with erotic or pornographic photos---and many of them will sue to stop such uses. You might win such a suit---in fact in my view you should wins such a suit on First Amendment and other grounds. But law suits are expensive--and the moment you are sued you will have to pay substantial amounts in legal fees to defend yourself--with no assurance of success. We are not talking about a couple of thousand dollars here---we are taking tens of thousands of dollars or more. It is up to you whether you want to incur these risks and costs, but if I were in your shoes I would not do so.