The first level, is when they simply take my work and upload it somewhere else, claiming it as theirs.
The second level, is when they take my work, edit it slightly and then upload it somewhere else, once more claiming as theirs.
The third level,  is when they take my work, and re-make one "of their own", copying my palette,  my style and everything else, then upload it as theirs because they think it's  fair-game because they "redid it!".

All three fairly common, all three fairly easy to deal with and quite honestly don't bother me  as much anymore, especially the first.
However, there's one last level, which annoys me the most, and that is...

When people try to "learn" from my work by copying it,  studying it, reproducing some of   its core essence, and finally producing something "of their own" that still, ultimately, looks like something I would've made while drunk. It holds my signature choices, my style, my train of thought and still it isn't done by me, neither am I mentioned anywhere as so much as a "reference".

I've encountered several of these people over the years,  most of the times they're brought to my attention by someone else.

It's not only that I dislike the use of my work in this way, it is that I fundamentally disagree with studying other people's art for your own.
...Imagine that you like an artist named Behemoth. You want to learn from them, but you don't  really  know Behemoth so what's your next step? Obviously, you download Behemoth's work and you study it, reproduce it, leech off of it until you can produce something similar yourself.

This is an act done by several young artists, and even older ones, mainly because there's a lot of teachers and art schools that tell you to do that exact same thing - learn by watching others! But there's a very vital reason why this does not work and it only turns you into a shadow,  a copy cat, a useless shell...

You've absolutely no idea WHY Behemoth chose to do what they did with their work.
None at all. If they use red  for something, you don't know why, if they did a certain anatomy skew, you don't know why, if they did a certain angle, you just don't know why. And if you don't know why an artist makes a choice with their work, then you won't know when to make that choice yourself. Maybe they did it because they like  it, because it's sentimental, because it means something to someone important to them, maybe because it sends  a hidden message, maybe because they just weren't sure what to do... you'll never know. Because that artist is not teaching you, you're just copying them.

If Behemoth made a series of unrelated artworks, which all had red in them somewhere,  then you'll  go right ahead and do the exact same! But you'll have no idea why,  or what it does  to the work, its implications.

You might think icons or pixel-art are very basic and simple, and that there's only a few ways to do them... but the truth is, there are as many as there are artists out there. And copying one of them? It'll show in your work. I've not only encountered several artists here that resemble my work shamelessly, I've found artists who resemble other great  iconists' works. It shows, people. And the reason it shows is because you don't have your own skill nor style and never will.

I didn't learn watching others, I didn't learn downloading tutorials, I didn't take some sort of short cut to pixel icons - I opened my program and I played with it, I made choices based on my personal taste, on my vision of the works, on the message I wanted them to send out, as little as they might be.

You, out there, who right know are reading this and have been using my or other people's work to create yours... I pity you. Because you'll never truly shake off my or that other person's style,  and while most of time I'll just shrug it off and ignore it, sometimes it's just too much and I've got to let the steam out.

Be your own person, your own artist. Do you like someone's particular style? Ask them to teach it to you, actually LEARN.  If they don't want to do it, then move on.

Last, but not least, to get my point across... "studying", "referencing" and "copying" other people's work in order to ""learn"" is the same as memorizing math answers for a test. Sure, when the time comes to take the test, you'll know the answers are 34, 55, 1990... but you won't know why those are the answers,  you don't know the process of the problem, and God forbid your teacher didn't change the questions, because then you'll be screwed, out on your own, and you'll have absolutely no idea what to do or how to do it.

TL;DR: someone told me I've a leech and while I refused to care or believe it, with each new work they upload, it resembles mine more and more. It pisses me the fuck off and I wish I could just erase their entire copy cat gallery. Woo!