I want to make a free browser game using the sprites from another game.

The project will not make any money and will be open source for the largest part.

It may never see completion at all.

So my question is this:

Can I play around (in a public space) using the sprites from a popular game for a free fan project? Do I need to ask the developer for permission? Can they sue me even though I am not making any money off of their assets?

I will describe a detailed scenario: You enter the URL diablo-fan-game.io in your browser and you see a character from Diablo 2, who you can send to run around. And all of this uses the graphics from the original game.

I'd say no, you can't do it. You do need to ask for permission. If you do it anyway, they will not sue you right away but legally threaten you first, demand you take it down, and then they'll sue you. It is not recommendable, why would you do it?

The fact that you aren't (planning on) making any money is irrelevant, you'd be using copyrighted material and copyright owners aren't going to like that.

Used to be on the FAQ.  The answer is: No.

3 hours ago, Jaret said:

The project will not make any money and will be open source for the largest part.

The Robin Hood defense does not work. It does not matter that you don't profit directly. Copyright infringement, trademark infringement, and similar IP violations are still unlawful even though you will never directly make any money from it.

Imagine that in other areas "Yes, judge your honor, I robbed the place, but then I immediately gave it all to the homeless and poor, and to starving children, so it is okay. Think of those poor starving orphan children that I fed with stolen goods, so I shouldn't go to jail."

There is only one condition under which you can use someone else's assets: if they allow you to use them. They can give you the right to use them, they can sell you the right to use them, they can make some other arrangement with you, but in any case the owner of the intellectual property (IP) needs to allow you to use it. If they do, you can use the assets. If they don't, you can't use the assets.

Everything else doesn't matter.
Fan game or not? Doesn't matter.
Open or closed source? Doesn't matter.
Commercial or free? Doesn't matter.
Nobody ever plays the game you make? Still doesn't matter.
The only thing that matters is "did the IP owner allow you to use that IP?"

Hi Jaret,

the company in question (assuming you really use Diablo2 assets) has rules for using their stuff in fan art, machinimas (even interactive ones and even ones that make (price) money) or other stuff.

I would suggest, that you read them carefully and if you have any questions left, send them an email or ask on their forums.

No one here is in any position to make a final and legally binding call on that case.

I found the answer to my particular question thanks to the answers here.

And also by finding this particular link: http://us.blizzard.com/en-us/company/about/legal-faq.html

I assume it should be the same for other games as well.

However, I found out that you can pretty much use assets from opensourced abandonware such as Siege of Avalon. Which would've worked great for me, in Diablo 2's place. But I decided to get my own assets.

32 minutes ago, Jaret said:

But I decided to get my own assets.

 In that case you should have a look at the rpg game dev humblebundle.

A few years ago I played FOnline, which is a Fallout 2 rip/remake  https://fonline2.com/en/

Recently I came across http://heroesland.com which is the same but with Heroes of M&M III

The latter is more like the thing I was thinking about making, although there was probably 1% chance for me to ever finish it. I'm looking for the licenses of both of those projects but I can't find it.