When you upload a new image, you should name it properly. For example: instead of Screenshot123123123.jpg, name it something like Episode 4 - Miku Nakano.jpg, or if the name is already taken, Episode 4 - Miku Nakano 2.jpg. It would help greatly with inserting existing images on the wiki.
Regarding the image quality, I'm curious about what device you normally use (mobile devices, PC), and if it's PC, how did you take the shot. I can give you a few advice on capturing high resolution/HD image.