Or make sure your images are better, visibly better, than the free ones........
This the real point - profesional photographers have to step up to the mark like all the pros in other fields that have gone before.
I have been writting computer programs for about 30years - in the begining we were in our 'ivory tower' and in demand and well paid. But now either the programs are prepacked for a few pounds or basically anyone can get a PC and cobble together a program. Is as good or as reliable - normally not, but its does what the user wants and that's all they are interested in.
If you are a good photographer you will produce images that appeal, images that say something special about the sitter, or the landscape, or the situation. This is why people pay for photographs and images.
A major split between Professional and Amateur photographers use to be the cost of the equipment, the processing equipment and skills required. But this is not so much the case now.
With news reporting the empasis is on getting an image to print or display as quickly as possible, and for unusual events, this is more likely to come from the people on the spot at the time, with the dreaded mobile phone.
One way to ensure that pictures do not get devalued is put inplace standard payment rules for every picture that is published/broadcast ... and everyone gets paid.