well jpeg files are compressed and have artifacts all over, you lose the pixel values, anyone who's seen more than a few can instantly recognise an image as a jpg because it blurs and even at high quality loses it's colour clarity and has blocks.
some suggestions, also I might as well say that hair is quite ridiculous if you intend to have it as an in-game character. it's volume is almost equal to a character.
the angle of the face on the large haired one is skewed for that facing angle, whatever you are referencing for the hoody jacket guy and chibi chick, keep using and try to stay consistent with, because the attempts on the left no offence intended are very weak colour and proportion wise, and that cyan guy has really strange legs and head, I did a quick attempt at depicting more viable proportions, the colour choice is decent on the girl
also your tiles don't tile too well. if you are using a program that has image manipulation tools you should try offsetting the tiles 50% you'll easily identify what's tiling well and what's not, alternatively and additionally you can tile a 3x3 grid with your tile to identify issues even more so, try editing the central tile, and if you edit one corner and it overlaps onto another you can copy the adjacent corner to the relevant corner on the central tile. I'd illustrate but I don't have the time.
what was your source/reference for those tiles if i may ask? the clustering on grass in particular is quite good and it tiles perfectly unlike the other two.
