Tidypics supports 3 image libraries: default is GD php extension (which is required to be available by Elgg core). And then there's the Imagick php extension (which you would have to make sure it's installed in your XAMPP environment). Lastly, there's the ImageMagick command line option which makes use of the convert command available within the ImageMagick package. The path to the convert command would only be necessary to provide if you want to use the ImageMagick command line tools.

I have to admit that I can't tell for sure if the ImageMagick option works on XAMPP/Windows. I never tried it and as I have no Windows I couldn't even try it. If you provide the full path to the directory where the convert command, i.e. where you installed ImageMagick to - try also with a slash at the end of the path - it either works or it might be the confirmation that it does not work on Windows. You can also try the path on the ImageMagick tab where you would get some version information provided by the convert command if it's found at the path and can be executed.

If the ImageMagick command line tools option doesn't work on XAMPP, you might try to get the Imagick php extension option to work as it's at least better than the default GD php extension because the latter has quite high memory consumption for resizing images with a high resolution. The other two image libary options don't have these memory issue.

Thank you, iionly, for your detailed response.

I installed the ImageMagick PHP extension and everything appears to be working fine.
The TidyPics Server Information tab displays:
             imagick    Enabled    
             exec()    Enabled    Required for ImageMagick command line

My site's production server is Linux, so the ImageMagick path will probably resolve correctly. If I do manage to get the ImageMagick command line tools working without the PHP extension, I'll post the results.

Thanks again.