This is an interesting subject. I have a lot of thoughts on this.
I found one of my own photos on somebody else's website, recently. I prepared an email in my head and was going to send it, but the next day it was gone... maybe she was paying attention to Google Analytics?
These days I'm trying my best to straight-up
copy from my Sull's Ornamental Penmanship anthology, as I'm trying to improve and refine what I'm doing and make my writing, as much as possible, like some of my favorite Penmen's. I'm trying to get all the traces of my 'handwriting' out of my calligraphy, if you see what I mean. One's personality always comes through, I think, but I'm trying to understand and embody the basics in a better way. The personality will always show eventually, I suppose, but I'm interested in technique right now. When I have any time to practice, that is what I'm up to.
When it comes to *current* artists or calligraphers, whenever what I've done something that was inspired in any way, or reminds me in any way, of the work of a living person, I always give credit. I've been inspired by some of Barbara Calzolari's beautiful banners (this is a common illustration in calligraphy), but I never actually tried to draw one until
her banners made me care about them. (In the one and only broadpen class that I ever took, my teacher used them in a heraldry-like way on envelopes, but those didn't turn my head).
I learned some shapes in flourishing from Heather Held's videos, which I used on a holiday card, and I posted my attempts on IG and linked to her (and wrote her an email saying thanks). A while back, when a bride I was working for asked me to decorate her wedding food bar signage with some gold accents (I first tried to splatter them here and there like goldy stars or something, then I made little tendrils of gold around the ascenders and descenders), and finally I ended up trying to squiggle and dot them on the just on the black letters instead of on the white paper, to pick up and reflect a bit of light in a subtle way. Of course, the second I did that, I had a very clear image of one of Schin's beautiful photos, where she had done something very intricate and beautiful with pearls of white ink to mimic the pattern on a piece of china dinnerware (totally gorgeous), and I thought, "I have to show her this, lol"... Not the same thing as my little reflective "dots", but of course I tagged her right away on IG and laughed about how mine looked like a leopard.

I absolutely had one of Estefa's first show-and-tell posts in the forefront of my mind the other day when I was making some signage on black paper, and was trying to work out how to include a cat. Her Halloweeny-feeling poster for a theatre piece obviously made its mark on me and I would like to try to capture a feeling that I got from looking at that work, rather than an exact detail. Whenever I'm inspired by someone directly, I always would give credit. These are all the living people/IG/forum/FB friends that pop into my mind right now, whose stuff has inspired or influenced me.
I guess what I mean is I can feel a difference in between "inspired by" and "in imitation of". It bears mentioning even when you weren't
directly inspired by someone, but nevertheless it made you think of their work after you look at it. I saw another calligrapher in France use what is more or less an exact copy of a descender flourish that I regularly make on the little "r" in "Paris" the other day, but it's also kind of an obvious mark to make in a central, evenly spaced kind of place at the bottom of an envelope... just kind of looks like it belongs there. Like Erica said, different people using the same kinds of inspirations can end up making the same kind of mark. My own is based on something from the Universal Penman, anyway. I've had someone ask me to make an exemplar of an alphabet, so they can learn from it! That's funny to me... why would anyone... they just don't realize yet that there's a wealth of work by real masters to draw from.
So many masters to copy, so little time.

As for living people-- if you wouldn't show it to them happily, maybe you shouldn't do it?