A .cbr file is a file which contain a group of JPEG images compressed into a tar, rar or zip archive. So if you have a collection of images which you want to convert into a cbr format so as to convinently view in a sequential manner using a comic book reader, then do the following :

1. Collect all the jpg files and put them in a directory.
2. Archive the directory to a zip file using any compression software of your choice. Linux has a plethora of ways in which you can create a compressed archive.
3. Lastly, change the extension of the compressed archive you just created to .cbr so that it can be viewed in a comic book reader of your choice.