The cosmological importance of the Lyman-alpha emission line has long been demonstrated. It is a powerful diagnostic tool of star formation, especially at high-redshift since Lyman-alpha becomes the strongest emission line in the optical-NIR window at z>2.1. It can be used, in principle, to probe star-fomation rates, clustering properties, or to put constraints on the final stage of the reionisation epoch. However the resonant nature of Lya makes the above studies far from being trivial. Dust, ISM kinematics and morphology may regulate the Lya escape. We present here the results of our HST/ACS imaging compaign of six nearby starburst galaxies. The high resolution allows us to map the Lya emission variations at a very smalll spatial scale (~10 pc) and, combined with ground based data, to probe the role of the dust in Lya attenuation. It is found that dust is not always the main regulator factor and ISM morphology and clumpiness may play a more significant role. We found that the diffuse emission accross the galaxy body accounts for the bulk of Lya, and the escape fraction to be very low ( always below 10%). Therefore, cosmological quantities, such as SFRs, based on Lya alone, should be taken with caution.
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