HEEELP MEEE! please!

hey all! so I'm having a posting problem! I'll try to post a picture, and it'll load for a while, and then it will be done loading and say in red at the top "please insert a file". i mean, what on earth?! i think i have the pictures saves as the wrong file, so please- what do you save your pictures as before you post them? or if this has happened to you, do you know how to fix it? thank you SO much!

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