Often when I post-process my scans, I have a lot of debris to clean up out of my scanner. This comes with the territory of pencil work - I'm putting colour pencil drawings face down on the scanner glass, so bits of loose colour and dust and junk get in there, and then show up in later images. It takes quite a bit of work to fix the image and brush out those specks - as well as fixing any other glaring issues. I tend to save a lot as I go, so I don't lose progress.
Unfortunately, for about 3 weeks around the time I made this comic, I'd screwed up the settings in my image processing program, rather than saving at highest quality, I was saving images at lowest quality, and I didn't notice. The program doesn't show the crunched image inside it, it just saves it, and windows thumbnails are small... so I just didn't see that it looked funky until weeks later when I came to upload it to my website. I could fix it by re-scanning the original and doing all the work again, but that'd take forever (and I'd have to find the original drawing in my archive.) - so we're stuck with this. It's just one of these story comics though, I'd fixed it by the next one.
Sorry again. I'm an idiot.