beamer中暗背景插入图片
http://tex.stackexchange.com/questions/18685/techniques-for-embedding-images-with-transparent-backgrounds-in-latex
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You need the standard package graphicx to include the image. Loaded xcolor would also be a good idea.Here some examples which use a transparent test PNG I got from http://entropymine.com/jason/testbed/pngtrans/rgba16.png.
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For advanced effects like patterns and shadings I would recommend you PGF/TikZ (i.e. the tikz package).
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