In my almost 20 years of postcard collecting, I've never come across this style before. Very art nouveau, it's a collage of photo and illustration with blank space for the recipient's address (but no stamp area designated). Entitled "Cantilenes d'Amour" (Melodies of Love), verso we have an example: La Poupee, a musical collaboration between Joseph Vander Meulen and Camille Verhe. I found two obscure references to this couple online: a 1902 opera called Liva and a book called Melodies of the Heart published in 1905. So that does help date this postcard or 'carte illustree.'
Fine print at the bottom notes that this is a heliotype de graeve produced by Gand. Printing processes are too technical for my brain but my favorite postcard web site, Metropolitan Postcard Club of New York, says that "This European form of photogravure was mostly used for commercial printing between 1870 and 1914."
Please note that on my computer, the direct scan gave this card more of a blue-green overcast. The photo taken at the window more accurately captures the warm cream and sepia tones. Typical antique postcard size of about 5.5 by 3.5 inches, this card has a creased bottom left corner. But overall, for its age, it's well preserved.
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