What to use when hanging a picture on plaster walls?

Number of ways depend on if the wall is plaster board (dry lined) therefore hollow behind it of it its a plaster on a cement render (solid wall)

For plaster board wall there are rawl plugs that are specific to to job which when the screw goes in opened up 2 small plastic flanges to hold the plug in place. The other plug is a self tapping plug which you screw in to the plasterboard and it had deep thread's on it to hold it in place. A scree then is screwed in to the centre of this the other method for solid walls is to drill in to the wall with a masonry drill bit and place a plastic rawl plug in there.

All good home improvement and DIY shops sell these items - Also consider the weight of the picture as this will have a bearing on spreading the weight over more that one fitting

In either situation PLEASE CHECK FOR SERVICES behind the walls like gas pipes, water and electrics