To become dim or blurred; to lose sharpness so that edges or details are indistinct (applies to vision, photos, memories, etc.).
寝不足で目がぼやける。
My vision is blurred from lack of sleep.
カメラのピントが合っていなくて写真がぼやけた。
The photo came out blurry because the camera wasn't focused.
思い出が遠くてだんだんぼやけてきた。
The memories are distant and have gradually become hazy.