Rio de Janeiro - A Brazilian court on Monday rejected former president Luiz Inacio Lula da Silva's latest appeal against a corruption conviction that could see him imprisoned for 12 years, and doom a bid to return to power in October elections.The three judges at the lower appeals court in Porto Alegre unanimously turned down Lula's appeal, which had been made on technical grounds, of his conviction and sentencing, the official Agencia Brasil reported.In theory, the ruling meant Lula might have been ordered within days to begin his sentence of 12 years and one month for accepting a luxury seaside apartment as a bribe from a construction company seeking contracts with state-controlled oil giant Petrobras.However, Lula was handed a temporary get-out-of-jail card last week by the Supreme Court, while it considers his claim that he should be free until he has exhausted options at higher appeals courts.The Supreme Court said it will rule on this on April 4th, and that until then Lula can remain at liberty.Lawyers for the two-term former president and founder of Brazil's Workers' Party said they may appeal the result of the Porto Alegre court's ruling.The 72-year-old, who faces six other corruption cases, says the legal onslaught is part of a politicised campaign to prevent him from running in Brazil's presidential election this October 7.Despite his troubles, he has surprised many by holding a huge lead in opinion polls ahead of the contest.Barred from running?The other threat to Lula's comeback is a Brazilian law barring candidates with criminal convictions from seeking public office. Now that he has lost his appeal in Porto Alegre, that law should kick in.However, experts say that Lula's lawyers could yet challenge the law and at minimum start another prolonged court battle, leaving the ex-president temporarily free to campaign.Regardless of his fate, Brazilian media reports say that Lula's strategy will be to keep campaigning for as long as possible -- even from behind bars -- in order to maximise his impact on the campaign.If barred from being on the ballot, he'd then endorse a Workers' Party replacement at the last possible minute, according to media reports.In polling, Lula would come on top in a first round of the election and win the runoff against any other currently expected challenger. Currently, his main rival in polling is far-right former army officer Jair Bolsonaro.When Lula stepped own in 2011, he was Brazil's most popular president on record, having benefited from a commodities-fueled economic boom and winning plaudits for his social policies.However, he also has high rejection ratings and is blamed by the right and many in the centre for Brazil's slide into the mammoth "Car Wash" corruption scandal that has shaken the country over the last four years.On Sunday, Lula and his entourage were pelted with eggs and stones while on a campaign stop in the south of the country, his staff said."A citizen throwing an egg at an event with hundreds of women, including some carrying infants, has no conscience," an angry Lula wrote on his website. "They are vandals, fascists."