This article is from the comp.sys.acorn FAQ, by Paul Vigay with numerous contributions by others.
Version 1.13S of ChangeFSI now has the RISC OS 3.6 JPEG support built into it. However the code has been designed to fail 'gracefully' if the support code is not available in the OS. For instance when you run the software on versions of the OS older than RISC OS 3.6. In this case a blank white window is displayed.
To regain normal use of ChangeFSI go to the main menu and select Sprite Output instead of JPEG output. Next time you load a picture, or re-process the current one, an image will be displayed. The JPEG Output option is not greyed out because even though no image is displayed you can still save the processed file as a JPEG.
For those of you with RISC OS 3.5 the module can be obtained from Acorn's FTP sites at ftp://ftp.acorn.com/pub/riscos/releases/spriteextend.arc This can be softloaded in your Boot.PreDesk sequence to use it.
If you've got RISC OS 3.10 you'll need to load the "JPEGMsgs" and "JPEGRender" modules BEFORE you load ChangeFSI. These were available on Acorn User CD no.8 (inside the $.Boot.Newboot.!Boot.Resources.!System.310.Modules directory)