What is this?

Ubuntu is capable of handling rotating backgrounds, as is evident from a few default ones included with a new install. However, it is not readily apparent to a normal user how to take advantage of this functionality. It is possible to create a custom rotating background in Ubuntu without the need for any third-party software.

This form is intended to help you easily create your own rotating background for Ubuntu.

Instructions

Open the terminal and run the following command:
find '[image folder]' -regex '.*.[png\|jpg\|bmp\|gif]' > filelist

Replace [image folder] with the absolute location of the folder on your computer which contains the images you want in your rotating background. For exmaple:
find '/home/user/Documents/images' -regex '.*.[png\|jpg\|bmp\|gif]' > filelist
This will place a file called filelist in the folder from where you ran the command (probably your desktop). It contains a list of the absolute locations of image files in the chosen directory. Open this file and copy-paste its contents into the 'File list' box above.
Enter durations for displaying each image and the transition effect between images (both in seconds) in the respecitve boxes above. Also, select whether you would like the script to sort or randomize the order of files in the list.
Press 'Generate XML' to generate and download the XML file. Save this file somewhere on your computer (recommended in the image directory).
Right-click on the desktop and select Change Desktop Background, press + Add..., select All files in the drop-down, and navigate to the XML file you downloaded. (Alternatively, you can drag-and-drop the XML file into the background selection box.)
Select the rotating background you just added and Close the window.
Delete the file called filelist.

Notes:

You may enter '0' for no transition time. This results in an instantaneous switch between images.
Ubuntu will not modify the XML file, so simply adding a new image to the image folder will not cause it to be included in the rotation. You will need to re-run this script each time you wish to update the rotation list.
Since the XML file uses absolute paths, you may include the absolute locations of any image file on your computer. That is, the images need not be in the same directory. (A remote location may also work but has not been tested.)
You can edit the XML file to specify a different duration for each image and/or the transition between them.
The rotation continues from the beginning when it reaches the end of the file list.