I am making a simple mod in MCreator that adds a buncha things. I'm making a mob for a new dimension which will look like an aqua-themed ghast. So if anyone has the original ghast texture, please post it here.
The ghast texture is copyrighted by Mojang, you're not allowed to just share it online.
Then there are a lot of mods that should be taken down, as well as sites like the Minecraft Wiki (where do you think they got all their images of blocks, items, and mobs from? They even note that they are copyrighted - even ordinary screenshots taken with F1; "This file (or parts of it) is copyright Mojang Studios") Some even go so far as to claim that textures which are slightly recolored are in violation of the EULA (which includes just about every mod that adds new ores/ingots/tools/armor/etc):
These aren't just a few exceptions: almost every major mod includes infringing content, in some cases numbering 50 to 100 instances per mod.
Mojang also only says that mods shouldn't contain a "significant" amount of their copyrighted code or assets, without specifying how much is allowed, other than an entire working jar (aka "modded version") being illegal (many mods also contains parts of Mojang's code as well, for example, I often use it as a base for my own features and in many cases you have to use the same class format anyway for it to be compatible at all with the game):
Any Mods you create for the Game from scratch belong to you (including pre-run Mods and in-memory Mods) and you can do whatever you want with them, as long as you don't sell them for money / try to make money from them and so long as you don’t distribute Modded Versions of the Game. Remember that a Mod means something that is your original work and that does not contain a substantial part of our code or content. You only own what you created; you do not own our code or content.
That said, you can find all the textures inside the game itself; use a zip utility to open the jar in ".minecraft\versions\versionname", or make a copy of the jar and change the extension to .zip and open it like any other zipped folder; all the textures and other assets are located in the "assets" folder inside, categorized by type (e.g. the ghast texture is located in "assets\minecraft\textures\entity\ghast" and has two separate textures for the normal and shooting states).
Also, you could get around the need to include the ghast texture if you recolor it when rendering it, although all parts of the texture will be tinted; for example, this is my custom silverfish and endermite rendering code (note that this is for 1.6.4), with a single texture used for all variants (modified from the vanilla texture; the code itself is based on the RenderSilverfish class):
(copyright Mojang Studios as these are simply recolored/cropped versions of their assets, the code is also mostly the same as well; all the classes in TMCW that end with "Fix" or "TMCW" are based on vanilla classes, usually very heavily modified but still recognizable as the original code)
It would probably be allowed for mods, its like Mojang would sue someone for using a texture they made in a mod for a game they made. Its not like Re-Logic would sue someone for for using one of their AI's in a mod for their game.