Even if you have image editing software that directly supports WEBP format input / output, you still have the exact same problem, because (like JPEG) it's a los

Even if you have image editing software that directly supports WEBP format input / output, you still have the exact same problem, because (like JPEG) it's a lossy format which will lose fidelity with each successive generation of load / save over time. If you intend to edit an image, then the original (if possible) and it's edit should both be saved in a lossless format even if the final published output is saved in a lossy format. If no lossless format of the original is available, then the highest quality version of the original should be converted to a lossless format for "archival" before editing, and that copy should always be used for editing purposes, rather than piling loss upon loss editing the lossy format and re-saving. It's kinda like copies of copies of copies of MP3 audio. Eventually it becomes a soupy mess not worth using.