Answering a question from harishkumar09 that he posted in a pm. The mds file contains m.e.t.a.data about the ISO, but won't include information regarding the separate folder you have with the posters. So using the mds file as input won't include the posters.
You could extract the Audio and Video_TS folders from the ISO, then build a new ISO and add the folder with the posters in this new ISO file. Mount the ISO image file in a virtual drive like VirtualClone Drive to access the files within it. VirtualClone Drive is free to download and use.
ImgBurn can build a new ISO for you if use Build Mode and set Output to Image File. I think I'd put the poster folder within the Video_TS folder, where it would be ignored by any player, but it would still be available for you to find using a computer to access the files and folders within the dvd. This would work assuming the poster folder doesn't increase the total size of the compilation beyond that which will fit onto your target disc.