The subject property of Assets is intended to indicate the function of the Asset.
Example for possible values inside Property Subject:
Example of an Asset within a TradeXML catalogue:
<Asset source="Image_fridgeABC_1"order="1">
<AssetProperty name="type">image</AssetProperty>
<AssetProperty name="format">image/jpeg</AssetProperty>
<AssetProperty name="aspect">front</AssetProperty>
<AssetProperty name="subject">product picture</AssetProperty>
<AssetProperty name="description">front of the product</AssetProperty>
<AssetProperty name="resolution_category">low</AssetProperty>
<AssetProperty name="pixelCount_x">150</AssetProperty>
<AssetProperty name="pixelCount_y">150</AssetProperty>
<AssetProperty name="filename">fridgeABC_1_150x150.jpg</AssetProperty>
<AssetProperty name="filesize_kb">700</AssetProperty>
<AssetProperty name="identifier">http://www.server.com/images/fridgeABC_1_150x150.jpg</AssetProperty>
</Asset>
Full Asset Property and Value List
Open: TradeXML - Asset Properties Definition