First, try Find-A-Grave. If you are not a member, you can join and search for the cemetery that you need a photograph. If you do not find the one that you want, then create a file for that person and click on the link to request a photo of the grave. Find-a-grave will generate an email to volunteers who live in the area of the cemetery requesting photos on your behalf. Their websites is http://www.findagrave.com
Also, you could consider contacting a volunteer at Random Acts of Genealogy Kindness. Some of their volunteers do still photos of headstones. Their website is http://www.raogk.org/england.htm