Several points to keep in mind:

1. Copyright is awarded automatically these days. While some countries let you register for Copyright and many companies apply a Copyright notice, to make litigation easier, all it takes for something to be copyrighted is to make it. (unless you're in one of the countries that didn't sign the Copyright treaty, like Eritrea or Iran)

2. Copyright usually ends 70 years after the death of its author (in some countries, longer, for some very old stuff that was awarded Copyright retroactively, a bit shorter). If something's Copyright says a number higher than 1947, it's unlikely that its copyright has expired already.

3. If there is no note that says that something is free to use explicitly, it is Copyrighted. Theoretically, an author can also verbally tell you "sure, use this as you wish", but as they so facetiously say "a verbal contract isn't worth the paper it's written on." How would you prove in court that they ever said that, if they forget and sue you? How would you know what rights they assumed you'd be exercising?

4. Copyright explicitly includes creating derivative works of the copyrighted work. As such, you can not make works based on someone else's and just modify it and claim it as your own.

There are a limited number of circumstances where you can use copyrighted works you don't own: Some countries have "fair use" (mostly for press and quoting purposes), and there is also parody, but these are kind of hard to rely on, as each country defines their limits a bit differently. In any way, if you're making a game similar to an existing one, or a totally different game with the same graphics, chances are you aren't making a parody.

So in your particular case, it's pretty much impossible, as it's unlikely your game sprites are from a game that was made less than 10 years after the first computer was created.

NB - I am not a lawyer, this is not legal advice.

Several points to keep in mind:

1. Copyright is awarded automatically these days. While some countries let you register for Copyright and many companies apply a Copyright notice, to make litigation easier, all it takes for something to be copyrighted is to make it. (unless you're in one of the countries that didn't sign the Copyright treaty, like Eritrea or Iran)

2. Copyright usually ends 70 years after the death of its author (in some countries, longer, for some very old stuff that was awarded Copyright retroactively, a bit shorter). If something's Copyright says a number higher than 1947, it's unlikely that its copyright has expired already.

3. If there is no note that says that something is free to use explicitly, it is Copyrighted. Theoretically, an author can also verbally tell you "sure, use this as you wish", but as they so facetiously say "a verbal contract isn't worth the paper it's written on." How would you prove in court that they ever said that, if they forget and sue you? How would you know what rights they assumed you'd be exercising?

4. Copyright explicitly includes creating derivative works of the copyrighted work. As such, you can not make works based on someone else's and just modify it and claim it as your own.

   There are a limited number of circumstances where you can use copyrighted works you don't own: Some countries have "fair use" (mostly for press and quoting purposes), and there is also parody, but these are kind of hard to rely on, as each country defines their limits a bit differently. In any way, if you're making a game similar to an existing one, or a totally different game with the same graphics, chances are you aren't making a parody.

So in your particular case, it's pretty much impossible, as it's unlikely your game sprites are from a game that was made less than 10 years after the first computer was created.

NB - I am not a lawyer, this is not legal advice.