As described on the Items view page, you can show images from internet using their URLs. However, if you want to add images which should be used in the same way inside the app itself that is also possible by using iTunes for file transfers. So connect your device to your computer, start iTunes, select your device, go to File sharing, and select CSV Touch:
Just add your image files; above the file items_list.png has just been added. Then in your CSV file, use the address file://items_list.png and it will be shown inline similarly to web images.
When CSV Touch notices the newly added image, it will be moved to the Local media folder seen above. To remove internal images, simply delete this folder. Unfortunately you cannot open the folder in iTunes so in case you only want to delete a single image among many, copy the folder to your computer, delete it inside iTunes, and then re-add all the images you want to keep from the folder on your computer.
In the future, I hope to be able to use the standard iCloud drive way to add images, but currently CSV Touch is not hooked up to iCloud drive.