That bore does look worn, with the classic vertical stripes. It looks as if there may also be a ridge at the top of the bore, above the highest point reached by the top ring. If the ridge is small you may be able to remove its bottom edge with a scraper, rather than doing the job properly with a ridge remover. The problem with leaving a ridge in place is that it has worn to match worn rings and ring grooves. If you then turn it over with new rings, unless the ring grooves in the piston are worn to excessive width, the top ring will hit the bottom of the ridge and mangle the bottom of its groove slightly. Before doing anything, though, you should measure the side clearance between a new ring and the top ring groove. If it is more than the specified amount, you will need a new piston (as well as the loan of a ridge remover). If you turn out to need a new piston, it is much better to rebore the cylinder at the same time.
The usual method for evaluating bore wear is to measure the diameter, at right angles to the axis of the crankshaft, 1 cm below the top of the cylinder. There is usually a wear limit specified by the engine manufacturer. It is probably around 0.010". In practice the wear is concentrated at the top of the cylinder, on the major thrust side, so there is a taper in bore size of about the amount of the wear. The rings have to expand and contract each stroke by the amount of the taper, which causes wear in the ring lands (the sides of the ring grooves in the piston), as well as preventing good oil control. Also, if you are using steel rail rings like those used in cars, the oil ring expander is likely to suffer metal fatigue and break in a fairly short time. I once made the mistake of choosing the wrong design of ring expander when I put new rings in a V8 with 0.010" of cylinder wear. After 3,000 miles, five of the eight oil ring expanders were broken, and oil consumption (which had been considerable right from the overhaul) became so severe that it smoked and oiled some of the spark plugs.
