I am using the extension method ContentUrl in EPiServer.Web.Mvc.Html which works like a charm. I am having some issues with this when using ImageResize.net. In edit-mode it seems to add ,,6435 (Content reference ID) after the image. So /blabla/folder/hola.jpg,,5333. Is this by design and required by EPiServer somehow or is it a bug?
as far as I have been able to ascertain the behaviour you describe is intentional on the part of episerver and is not a fault. Linus Ekstrom of episerver confirmed to me the pattern of the edit mode URL form in the latter stages of cms 7.5 preview programme just before the actual release of cms 7.5. If you take a look at the code here http://world.episerver.com/Code/Martin-Pickering/ImageResizingNet-integration-for-CMS75/, you will see that the URL pattern for edit mode is deliberately being searched for and handled to overcome the problems it causes when using image resizing.net and the URL form hiding requests for images from the image resizing.net plugin.