Customizing RSS feed URLs with starter and ending item

Note: project involves viewing adult softcore occasionally. I have a free image host called picmecca.com. It has different picture categories and user is able to generate rss feeds of the pics inside categories. The category rss feeds work the traditional way, in which the newest pics are used in the feed upto the number of pics desired in the feed (For example, 20 newest items). Since some categories have too many pics (2000 for ex.) and some rss readers have limitations (they read 500 newest items and forget the rest, for example) this project is about: Giving the user the possibility to define the pic number to start from (starting rss item) and the last one (ending rss item). Sample rss url to display 500 items, from item 1400 to item 1900, from a category with 4765 pics: [login to view URL] The field to Define the starter and ending item #: will be added to [login to view URL]