It's avery long process. They don't have to have performed miracles when alive, or have uncorrupt remains, but after their death a miracle is usually sought as 'proof' of their sanctity. A 'devil's advocate' is appointed to find out all the nitty-gritty details of their lives & find reasons why they should NOT be declared saints. Some excellent people have been refused on these grounds. A person is first declared Venerable, then the process starts again & they MAY become BLESSED & only eventually (after years sometimes...and vast amounts of money) they may be declared a saint. In many ways IMO (& I am a practising Catholic) it is all very corrupt. Some people are declared saints because their organizations or religious orders can afford to pay loads of money to sustain the process...Others are refused on political grounds (e.g. Oscar Romero of El Salvador) but that's the way it is.