This was also my assumption. You can faintly see where the vertical white strips starts on both the bottom and top (See Zoomed Image for Reference). You can also faintly see the horizontal red bleed through the white vertical line which indicates to me that this was a physical alteration. Given the slight shadow casted by the bottom white vertical, and the neatness of the lines - I would assume that this was done with what is typically referred to as a Page Flag/Marker.
Looks to me like the image itself wasn’t edited, but they used red and white tape on the flag.
It makes it seem like it was edited, but it was physically edited.
This was also my assumption. You can faintly see where the vertical white strips starts on both the bottom and top (See Zoomed Image for Reference). You can also faintly see the horizontal red bleed through the white vertical line which indicates to me that this was a physical alteration. Given the slight shadow casted by the bottom white vertical, and the neatness of the lines - I would assume that this was done with what is typically referred to as a Page Flag/Marker.