Hi, the image you uploaded here is 800+ pixels, the texture you have in Unity is set to have a maximum size of 512, so if this source image is the one your using in Unity: Unity will resize it at import time, loosing information/quality in the process.
Also, when you display the image in game, it looks like the size is even smaller, like less than 100 pixels on screen. When down-sizing images, information is lost, example: the black lines around the red icon might be totally lost. To verify it: try reducing the size of your source texture to the size it has on screen using your favorite 2D software but using the simplier “point” filter (or even bilinear may show the problem too). You should have the same result as in game.
It’s best to have a texture the size it will be displayed on screen (or as close as possible).