Plugin not working ? I am describing the issue below

Hello. I have set the png watermark that i have in my media folder, and i tried to apply it it in bulk to my old uploaded pictures. I got an error in the middle of the process and now i dont know if i have a watermark or not on my pictures. I have manually checked all and no watermark on any of my existing pictures. They are .webp files. My question is, how do i know if i this plugin watermarked any of my existing photos? Apparently there is no visible watermark on any of my phothos, thank you in advance.