Participants claim a tripcode preferably just for this challenge and post their image with it, also add a caption - no description. With the tripcode only participants each are asked to up-vote 3 foreign images at max. Participants are not allowed to participate with several images or exchange the posted one. The challenge is limited to 15 participants images, it ends about 48 hours after the last participating image-post where the votes at this time define the winners.
For images there are no further restrictions in addition to the /p/ etiquette. The up-voters decide according to their own expectations, for example if they recognize a wide interpreted topic, allow or disallow composings, aim for present emotions, technical correctness, graphical/structural elements and so forth.

Be polite and fair, also just bump this thread for your personal interest.

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Topic highs and lows aims at illustrating differences, this may be a simple thing. Intuitively perhaps many people think of the stock market and economic development, but images may also show dimensional differences, social differences, distinct light situations, shapes of buildings or landscapes showing the same depth and height. The difference is in relative terms which of course can also be construed ironic like something underwhelming, next to something which is even more underwhelming.
Let yourself be inspired by this proposal, it is not a guideline.