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are the photos really large or are you talking about a large grouping? if not i cant see why they would need to hung above where you can reach. the middle of the picture is usually said to be about 58 inches from the ground level, that is average eye level, it can be adjusted if you all are way taller or shorter than that. but yeah for large grouping the ladders that are made for stairs are the way to go.
hee is the kind of ladder that works with stairs http://www.homedepot.com/Building-Materials-Ladders-Multi-Position/h_d1/N-5yc1vZasew/R-203460212/h_d2/ProductDisplay?catalogId=10053&langId=-1&storeId=10051#.UEInSkLWpRo
or there is a thing that can be added to one leg of a lean to ladder http://www.homedepot.com/webapp/wcs/stores/servlet/ProductDisplay?productId=202071192&storeId=10051&langId=-1&catalogId=10053&MERCH=REC%2d%5f%2dproduct%2d1%2d%5f%2d100658394%2d%5f%2d202071192%2d%5f%2dN#.UEIorULWpRo
there are a few products that help you put groupings together in a nice way if you feel overwhelmed by that, but most are pretty costly.
here is a nice guid to how to hang pictures, i used the math to hang a whole house of fine art when i helped move a family member and it was super easy once you got used to it and the rooms looks amazing, it was the right height in all but a very few very tall pieces. http://www.stellersgallery.com/resources/howtohang.asp
i also found this interesting tutorial after a quick google search http://www.scrapnframes.com/SITE_EN/FRAMING/StairwayArrangement.html
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