A graph or two are worth a thousand words. This is what a stolen election looks like in all it's pretty colors when you compare the 2005 elections results to the last weeks' election results' of candidate Mahdi Karroubi.
From FiveThirtyEight's :
Karroubi was the leading reform candidate of the 2005 election cycle, in close competition with one other reform candidate, one centrist, and two conservatives, including Ahmadinejad. He won in 11 of Iran's 30 provinces, the most of any candidate that year, and was within 2 points of advancing to the run-off. It was a strong showing, which encouraged him and his backers to challenge Ahmadinejad again this year.
Polling put his candidacy at around 7-10% of the national vote this time around, with the strong incumbent expected to pull more in the first round than he did in 2005 (19.1%). Karroubi's numbers in his provinces of strength were better, with polling regularly put him at around 20-25% in his home region, with particular strength in the provinces of Lorestan, Ilam, and Khuzestan. This is where the provinicial results get fishy:
Not only did Ahmadinejad beat Karroubi in his base of support, he crushed him beyond all recognition. Karroubi's share of the vote in Lorestan was cleaved by a factor of ten, and in only two other of the provinces did he break above 1%. Even with a consolidation of conservative support, and possible defection of Karroubi supporters to Mousavi (who was likely perceived as the candidate more likely to win) this large of shift is hard to imagine.