I restored the defaults and added the img and iframe like you showed me. but on the browser side the HTML doesn’t show the added img and iframe tags 
Allowed HTML Elements
p,br,strong,em,span,div,ul,ol,li,a,h1,h2,h3,h4,h5,h6,address,pre,table,tr,td,blockquote,thead,tfoot,tbody,th,dl,dt,dd,q,small,strike,sup,sub,b,i,big,small,tt,img,iframe
Allowed HTML Attributes
*.style,*.class,a.href,a.title,a.target,img.src,iframe.src,iframe.width,iframe.height,iframe.allow,iframe.allowfullscreen,iframe.frameborder