Multiple times, Minecraft player skins in their flat .png file form, have been appearing over the Minecraft window, while playing on various servers, and the only way to get rid of them i have found, is by maximizing and minimizing the window multiple times, or restarting the game. Hear is a more detailed description.

• Has only happened to me while playing on servers, examples of the servers I have played on where this has happened include, mc.minehut.com, mc.hypixel.net, and us.mineplex.com
• Image covers entire window, including the pause screen, hotbar, ect
• Images has always been a different image, but always that of a minecraft player skin,
• None of the images that have appeared have been files i have saved to my computer, or used on a different computer, with the same minecraft account
• The only ways I have found to get rid of the images, is maximizing and minimizing the window once to about three times, or closing minecraft and relaunching it