The distribution of bismuth in InAs1-xBix/GaAs quantum dots is analyzed by atomic-column resolution electron microscopy and imaging simulation techniques. A random Bi distribution is measured in the case of <0.03 ML/s Bi flux during the InAs growth with no significant variations in the shape or size of quantum dots, resulting in a low redshift and the degradation of the photoluminescence. However, for a 0.06 ML/s Bi flux the lateral indium segregation into the quantum dots is enhanced and Bi is incorporated inside them. As a result, a strong redshift and an increase of the peak intensity are found in this sample.