When running into this kind of doubt it's often useful to think in terms of real objects, their behaviors, and responsibilities, so you could ask yourself:
Do pictures look up file locations? Doesn't sound like the behavior one could expect from a
Picture
orPictureFile
.Is a picture responsible for looking up the location where it is stored? I don't think so, maybe a
PictureLocator
,FileLoader
, etc.
Whenever such a method belongs to a service layer, application layer, or even a data layer, depends on your architecture. Although I don't know the details, it seems like quite a simple method to be something of entity in the service layer.