I want to report an error or a problem

Hello, I am struggling to upload a photo for the cover of my showcase. The file is a jpg and I got it down all the way to 500KB but it still claims that the file is too large and the limit is 15 million pixels per image. Could you please advise me in what format should the photograph be?
Many thanks

k.cacikova0620231@arts.ac.uk

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