If the height is fixed, it will not maintain the aspect ratio, set them to the maximum you want, and it will maintain the aspect ratio.
.ArtistPic { max-width: 720px; max-height:660px; }
Edit:
Take a look at your image tags, they can set the width and height on them. If so, you will need to remove them.
<img src="image/path" width="250px" height="3005px" alt="valid image"/>
If it has width and height on it, you cannot fix it with css.
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