I have a page for wallpapers and i got a question regarding seo. currently i have removed the Prefix wich was .PHP so that the URL is mypage.com/category/imagename/ What i also did is that i added to the url and the name, the size of the image so that it became mypage.com/category/imagename_x_1600x1200/ where x after the imagename is the number of the image in that category. Is this good ir bad to add the size in the URL? it's in the description of the image but is it bad to have it in the URL?
By adding the image size to the image name (=keyword) you decrease it relevance for the keyword. I would not do it. To make the final decision, the right thing to look at your competitors for your keywords. Also is important except alt tag, near each picture write a short text about this picture.