Creating Multiple Sizes of Thumbnail Images - Hiranyaloka/Documentation GitHub Wiki
You can generate different-sized thumbnails of images in MT4 using the AssetThumbnailURL tag.
<img src="<mt:AssetThumbnailURL width="100">" alt="tiny size">
<a href="<mt:AssetThumbnailURL width="640">">small size</a>
<a href="<mt:AssetThumbnailURL width="800">">big size</a>
<a href="<mt:AssetURL>">full size</a>