Good pic! Look at the small, shiny strike plungers on the outside head of the rail, which were usually arranged in a pair. When the wheels hit these, grease is pumped onto the inside (gauge face) of the rail: this one doesn't appear to be connected. You can hear a definite "ching" when wheels make contact with them.
There are several different types, some more archaic than others. I used to have pictures (for former professional reasons!) but I'm not sure where they are now. Look for the variants that sit almost buried in the ballast or the taller, cylindrical drums, which are considerably easier to model:
(Common source image from https://en.wikipedia.org/wiki/File:Rail_track_lubricator.jpg)
Note the ancient lubricator with modern, "fastclip" track!
These things need constant maintenance and often malfunction: they either pump too much or insufficient grease when this happens. The gauge face of the rail is always shiny black ahead of them in the direction of traffic: trains obviously run left to right in the above picture. If it's broken, there will be grease everywhere in the vicinity of the pump!
Rail lubricators ("greasers" to the maintenance gangs) are normally located prior to the start of the transition (where cant starts to be applied, track goes from straight to curved), of a curve so that most of the rail in the curve is able to be lubricated. The one in the above pic is actually in the transition which again, is not uncommon. I have also seen very long curves where "booster" lubricators were fitted to aid greasing. They are also only fitted to the high rail of a curve, which is the rail that becomes gauge worn in normal traffic. Single or bi- directional lines may have one at either end of the curve. In reverse curves, you may spot lubricators almost opposite each other.
Some types also possess different size drums for capacity reasons. The larger drums are often fitted where access is difficult for gangs to fill them up, for example on viaducts or embankments or in cuttings. Those types (such as the one in Pete's picture) which foul the track are painted yellow to assist sighting for tamper operators etc. and are often repainted when they become dirty.
A good curve maintenance team ("grease gang"!) will be equipped with copious spares and tools, good overalls, grease barrels, degreasing fluid, yellow and black paint and endless patience! They used to repaint the cant markings on the curve while they were there, under lookout or T2 protection, although it wouldn't surprise me if much of this work is now undertaken at night during T3s.
If you're a lubricator rivet counter , BR demonstrated considerable regional variation, although I'm sure Network Rail now have more modern, standardized types... said with a semi- straight face...
I used to try and standardize on a particular type on a certain branch wherever possible. The gang may attend to several in a day, working down the track. Maintaining the same type on the same day makes stocking the van considerably easier.
Sorry to ramble on but Pete's pic brought back some long ago memories!
[Edits for additional info: started as a short post, ballooned as memories came back!!]