The trouble looks like the image isn't square and the browser adjusts as such. After rotation ensure the dimensions are retained by changing the image margin.
.imagetest img {
transform: rotate(270deg);
...
margin: 10px 0px;
}
The amount will depend on the difference in height x width of the image.
You may also need to add display:inline-block;
or display:block
to get it to recognize the margin parameter.