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Alt tags are more important for SEO as far as I know. I think titles do help, but it can get complicated really fast if you want to have unique filenames for several languages. I'd go with the unique alt tag solution. A strong site structure, some decent backlinks and a strong, optimized site are going to have much more of an impact on rankings anyway. Then again, if you have just a couple of images and are really concerned about everything being perfect to the last detail, you could use different image filenames.

Thanks for the answer Robert. Yes, I´m using hreflang correctly and the serps of the different country versions shows the corresponding country folders. i.e. google.co.uk shows results from the uk folder, google.fr shows the fr folder,… The redirect only occurs on the homepage from mydomain.com to mydomain.com/fr, mydomain.com/uk,….. If a user is in the French folder but is located in London isn’t redirect to the UK folder.