Blue ring from the CFHTLS with a neighboring galaxy of a similar color in the observed projected plane (left panel). Without mask, sl_fit identifies this piece of environment as a bright lensed feature and searches for an incorrect lensing configuration (top right panel). Here, our standard masking eliminates most flux from the blue galaxy and thus helps the modeling to focus on the actual lensed flux (bottom right panel). As in Fig. 5, we show in each case the original image where the deflector has been subtracted in the g band, and the gravitational arcs or ring reconstructed by the model with the critical lines (in red).