Quoting wikipedia:

Quote - Many JPEG files embed an ICC color profile (color space). Commonly used color profiles include sRGB and Adobe RGB. Because these color spaces use a non-linear transformation, the dynamic range of an 8-bit JPEG file is about 11 stops; see gamma curve. However, many applications are not able to deal with JPEG color profiles and simply ignore them.

Almost all apps ignore the color space and assume it's the standard sRGB. In any case, whether sRGB or Adobe RGB, neither are linear.

I could write a shader to decode ARGB in Poser but I never bothered.

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Renderosity forum reply notifications are wonky. If I read a follow-up in a thread, but I don't myself reply, then notifications no longer happen AT ALL on that thread. So if I seem to be ignoring a question, that's why. (Updated September 23, 2019)