* STYLE (URL to CSS file, by default is none, no stylesheet link is set)
If it is JPEG XL, then, for compatibility reason with non-bleeding edge
-software, alternative format is generated too: either JPEG (if JPEG XL
-contains losslessly transcoded JPEG), or PNG (leaving off the alpha channel).
+software, alternative format is generated too (unless NOALT environment
+variable is set): either JPEG (if JPEG XL contains losslessly transcoded
+JPEG), or PNG (leaving off the alpha channel).
If image file has corresponding .txt/.html, then it will be included on
HTML page.