Richtext Redactor Field - Standard Layout does not show image button
Tested and it works fine for me locally with the stock Standard.json config of

{
    buttons: ['html','formatting','bold','italic','unorderedlist','orderedlist','link','image','video'],
    plugins: ['fullscreen','video'],
    toolbarFixed: true
}


I'd make sure you don't have any other plugins installed that might be interfering and that you've actually got the 'image' value listed under your buttons: key.