Hello,
phpdcx parses the URL to be able to get the image type, using exif_imagetype when no extension is found as it's the case of stream images.
We have run the internal tests and all cases return the correct output. Although using a URL such as /image/123 is a good alternative, if you are using a public URL, please send it to contact[at]phpdocx.com and we'll test it. We have also moved the topic to the dev team to do more tests.
Regards.