I obviously lack a basic bit of understanding of this method...

This works:

<img src="@Url.GetCropUrl(Model.Content.WtImageBackground, "L")" />

(Where WtImageBackground is the alias of the image and "L" is the crop name.

However, when I call the children of the current page, this does not work

var wtChildren = Model.Content.Children();
                                    foreach (var wtChild in wtChildren)
                                   {

                                        <img src="@Url.GetCropUrl(wtChild.GetPropertyValue("WtImageBackground"), "L")" />
                                   }

However, if I only call wtChild.GetPropertyValue("WtImageBackground") I get the numeric reference of the image, much the same as I do with Model.Content.WtImageBackground.

Any thoughts on getting this working or any links to a resource that might give me a thorough understanding of Url.GetCropUrl would be appreciated.