To post a screenshot in Safari, select "Upload File":
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Then select "Choose File":
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Go to Photo Library:
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Choose "Screenshots":
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Select your screenshot with the bubbles:
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It will start loading. When it has finished, you'll see a small picture of your screenshot. Choose "Full Image", then post your screenshot:
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The screenshots are from an iPad. The way to post them is the same on the iPhone.
Sending them via pm is also the same.
Hope that helps.