You can use sprite rips. It only makes sense to use them if you are making a texture pack based on a video game. I mean how better to recreate the look of a 16 bit game than to use the actual textures from the game itself. I personally ALWAYS use official sprites as much as possible for my game related texture packs to stay as true to the source material as possible. You will definitely end up tweaking most sprites anyways to make them look right so very few sprites end up 100% exact to the source material. It can be a pain converting sprites to look right for your purposes though lol. especially if the sprite you want is say for a terrain texture of wood planks and you use the textures from an old RPG on the Super Nintendo. Well the MAJOR issue you will run into 99% of the time is that everything in most RPG's is viewed in an overhead perspective and therefore will be greatly askew for your purposes so you have to redo the texture just to make it look like you are facing it head on instead of at a top down angle. I hope that made sense I tend to ramble.
Long story short. Yep use sprites but do your best not to make a pack similar to others. I noticed a bunch of Legend of Zelda texture packs pop up after a few people liked mine.
