How to attach an image directly inside iOS Mail app while writing an e-mail?

Solution 1:

Press and hold anywhere on the text area. A contextual menu will appear. If there is no text on the message, the option to the right will say "Insert Photo or Video".

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If there is text, the options will be "Select", "Select all", "Paste" and an arrow. Clicking the arrow will show "Insert Photo or Video"

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Click on it and select the Photo or Video you would like to attach.