bonjour,
c'est fiscal, les "proprietary" timbrent ce qui est non-officiel (les "documentary" timbrent les actes officiels).
Wiki : Among the more notable instances of tax stamp usage occurred in the photography trade. As the Civil War progressed, the demand for photographs of family members, soldiers going off to war and returning war heroes increased dramatically, but not without the notice from the Federal government who saw the advent as an opportunity to raise much needed revenue for the war. On August 1, 1864 the Internal Revenue department passed a 'photograph tax' requiring photographers to pay a tax on the sale of their photographs. By 1864 there were no 'photography tax' stamps issued, so other stamps were substituted, typically, the proprietary or playing card revenue stamps was used, usually affixed to the back of the photograph. Already burdened with high overhead costs and scarcity of materials because of the war, large photograph companies organized and petitioned Congress, complaining that they were shouldering too much of the tax burden placed on the public. After exactly two years their constant efforts resulted in the tax being repealed on August 1, 1866.
D.
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dubito, ergo sum