The built-in controls resolve the path internally and you should not have problems with this.In controls like GenericContent, Sitefinity Image we use Telerik.Cms.Web.LinkParser
that gets sfref
attribute ( which format is [Provider]ID) of the item and then resolve the correct path.
"width: 200px; height: 200px;"
We had similar problems with versions before 3.7 SP2 ( there is SP3 available now).
In case you have a custom control you need to get the parent of your IContent item. The parent is actually the library (ILibrary), so you can get the correct library name.
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