Determine whether the uploaded file is an image. If it shows the width and height of the picture.

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<FORM name=form action="" method=post encType=multipart/form-data><INPUT onpropertychange=document.all.aaaa.src=this.value type=file name=upload><BR width: INPUT name=W high: INPUT name=H BR><INPUT type=submit value= submit><IMG style= POSITION: absolute; TOP: -100000px onerror='alert(wrong type or target does not exist);' onload={document.all.W.value=this.width;document.all.H.value=this.height;} name=aaaa></FORM>

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Source: 51Windows