I've recently encountered a bizarre situation where a grey bar started showing up through all my generated images. The original image is clean and as it is being compressed a gray bar is added to all of the small images, thumbnails etc.
I've not altered any of the CSS and am pulling from parent Blank. I switched back to the parent theme to test if it was something in the theme. I also reverted back my files to when my images did not have the grey bar running through them. Neither of these efforts resolved the issue.
I had the DB reverted back to the date when the images were clean and this did fix the issue.
This made me quite curious to figure out what about the DB was causing the grey bar as I am about to begin importing products again and also would like to go to a flat catalog as I heard would make for a faster user experience.
In developer mode I switched to flat files but double checked and all seemed to be fine. It was only when I started importing products again after switching to flat file that this issue began. I am wondering if there is something in my import that could have caused this with having moved to flat files? Or if anyone out there might know how images are compressed and how reverting the DB might have fixed this issue.