That is a tough call. I love your long hair. I'm also a fan of short hair ...even really short. If you're just doing it for modeling, I'd say know. I'd suggest being more creative with your hair instead of cutting it. If you want to do it for yourself in everyday life....that is your personal decision on how you want to look.
I feel your dilemma. I want to do something similar next year in cutting off my locks. I love doing art nude modeling and I guess it all depends on presentation. With alt modeling, I guess it would depend on the clothing, make up, and photography.
IMO You shouldn't dye it pink if you want to keep art nude modeling. You can get some work with it short and pink in that genre but it would limit your market. If you wanted to go full blown alt model with the wardrobe, piercings ect.. you could probably get plenty of work if that is the direction you want to go.
I would work with you either way.
I prefer prefer long hair myself but that is just me.
The haircut and natural colour you have now is completely marketable. It always you do a variety of types of work. If you choose to go for the short dyed red style, know that your work might be limited to more alternative types of work only. If that's what you're looking to do, then I don't think you need to worry about not having tattoos and piercings. There are some great alt models who have none.
Every model I've known that have done such a dramatic cut has always regretted it! INCLUDING your hair is too dark naturally to go lighter on such a grand scale, you will end up frying it. seriously frying it and you will have to wait years before the damage hair is grown out and trimmed away ...its a holy mess.
So call up a few high end hair style shops in your area and get their honest advice, and what the actual consequences might be.
If you just want the illusion of shorter hair Rachael / just braid or tie it up and / or try a wig ~ (there's no easy way back after you 'chop chop) and don't let mere trends cloud your decision.
I think the longer dark hair would look better than short "punk" unnatural red hair for black and white photographs (clothed and especially fine art nude). I think if you had the shorter alternative hairstyle, it would label that lifestyle on you from the audience's perspective.
Since you don't have any tattoos or piercings, it may be hard to fit that genre.. but i'm sure there's genius creativity for everything if you wanted to go down that route.