stegoeasy
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hackerlab
Task: two PNG files appear ordinary, but one black companion image hides a sparse alpha-channel mask instead of visible content. Solution: inspect RGBA values, threshold the nonzero alpha pixels, and use that mask to reveal selected words from the other image, which combine into the final flag.
$ ls tags/ techniques/
alpha_channel_extractionmask_overlay_reconstructionselective_text_reveal
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