Well, SebastianG63, let me be blunt. You are misinterpreting your results.The facts of the matter are If you are uploading an image larger than 64x64 pixels and see that it looks better, it is nothing more than as a result of the image scaling process of size reduction done by SL when you upload the file and the system converts it for storage (essentially you're getting an anti-aliasing benefit).
If you create your 64x64 textures appropriately before uploading them to SL they should always look better because there is no scaling happening when the file is uploaded. For instance here are three sample images.
1) A 256x256 image the square and circle are squiggled (created to dramatically emphasize my point).
2) When I reduced it to 64x64 as the SL client would, it's a miracle, the box and circle now are clean lines and look better! The scaling has smoothed the edges just as expected.
3) But! If I craft the image at 64x64, taking pains to create my lines precisely, it looks even cleaner.
So, in reply to your last snarky sentence, I would suggest that until you learn about how real world image processing works (or even image processing for SL content) you might want to consider not coming into these forums and making demands when you don't know what you're talking about.
There are plenty of people here that are wonderfully helpful and patient in explaining things, but not when you come in on the attack.