tagging images

so ive got hundreds of pictures in my computer and decided to tag them to sort them all out as it always takes me way too long to find what im looking for but for some reason there are a lot that i cannot tag- theres no “add tag” at the bottom, and even when i go into properties i cant type it in there
at first i thought it was the format as some are png but there are also jpg,gifs and other various formats so cany1 help me resolve this issue?
Answer #1
im gonna use this thread seeing as that person has been banned im having a similar problem im unable to tag some downloaded images, i am using vista- dont know if that matters or not