With Sitefinity RC2 we introduced custom fields for objects that inherits from Telerik.Sitefinity.GenericContent.Model.Content which will allow you to associate some custom data with your items. You can use the fluent API in your custom implementation to get the custom filed values
var imgs = App.WorkWith().Images().Where(img => img.GetValue("longt") == "somevalue");
The Content item has extension methods that you can use
GetValue - gets the value of a dynamic property.
DoesFieldExist - extension method that determines if the dynamic field exists on the type
SetValue - sets the value of a dynamic property of data item to a different value.
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