Image Brightness Across Platforms

I have been using using Linux as my main operating system for a little over a year after using a Mac. Recently I sent a digital photograph that looked fine on my system to a PC user. The user complained that all shadow detail in the image was lost.

When I used a Mac, it was not unusual for images to appear brighter on Macs than on PCs. Is there a predictable relationship for image brightness between images on Linux machines and those on PCs, or is it determined by hardware or other factors?

I think it may be just your monitor brightness