These three pictures are of pistons from engines which have lost compression on one side (usually left side). There are may schools of thought as to the pro's and con's of using unleaded fuel with an additive or the new British fuel LRP (Lead Replacement Petrol). Until LRP is given a BS(British Standard) number, most advice is to tread carefully experimenting and talk to other drivers of same cars. For more information click here

My advice is to avoid long distance constant speed running (i.e. motorways) and keep to the A roads and make sure that your tappet adjustment is checked and adjusted each year, together with a small tightening of the cylinder head
Note: These are my personal observations and comments

The crown of this piston was impacted by the broken parts of piston rings being trapped in the cylinder head when the piston reached "top dead centre"
You can see from this picture that the top ring has broken away from the piston and caused damage to the top 10mm of the side
I don't know how hot aluminium has to get before it melts, but this piston had a melted segment around the centre piston ring.