Photos dragged from iMac Photos to desktop won't upload
If I drag a photo from the Photos App onto the iMac desktop it deposits a JPEG file, with the extension .jpeg. I do this to (eg) upload photos to a web site, or email them to non-Apple users. But the JPEG file is rejected by websites like Gumtree, Snapfish etc and unreadable by other users.
If I change the extension to .jpg it is still not usable. To make it usable I have to open it with Preview and export it as JPEG, in which case the resulting file has extension ".jpg" and is usable. On the other hand, if I export it from the Photos App using File > Export, as JPEG, it creates a file with extension ".jpeg" which is uploadable, but with a different colour profile and 5 times the size!
Does anyone know why the drag to desktop from Photos creates a jpeg file incompatible with non-Apple devices? I cannot find any setting for Photos to change the jpeg format it creates on export.
iMac 27″, macOS 10.15