Putting a grid on a reference image

[jebbasha]

Thanks to everyone for so many tips posted on this forum. I am from Italy worldcams.tv/italy/venice/rialto-bridge and I am an often guest here. I regularly follow new discussions and usually find a lot of useful things for myself. And this thread is one of them. I am not very well-versed in this respect, but I appreciate many specialists share their thoughts.