I. INTRODUCTION The electromagnetic properties of spin-1 particles ( V ) can help us to understand the symmetry structure and interactions of the fundamental particles. For example, considering V as a stable state, the electromagnetic properties of the W gauge boson are predicted by the symmetry structure of the standard model, while for the ρ meson several predictions exist, based on effective models of the strong interaction binding the quarks [1–5], and from lattice-QCD [6, 7]. However, they are not stable states. Therefore, in order to draw definite conclusions, a complete study of the additional effects due to their instability is mandatory. The proper theoretical description of such states requires to incorporate their unstable features (parameterized by their finite decay width, Γ) in an electromagnetic gauge invariant way. To do so, several schemes have been developed, we can mention, for example, the so called fermion loop scheme [8–10] and the boson loop scheme [11] (suitable for the W and ρ bosons respectively), which consider that Γ is naturally included in the calculations by taking into account the absortive contributions in the electromagnetic vertex and in the propagator. Under these schemes, the electromagnetic vertex V V γ is modified respect to the tree level form in a non-trivial way. This implies that the electromagnetic structure itself suffers modifications. In the present work we analyze the most general results for the electromagnetic vertices obtained in the loop schemes, which include the mass of the particles in the loops, and extract the expressions for the modified form factors. In order to exhibit the size of the corrections due to the unstable nature of the particles, we compare our results for the magnetic dipole moment (MDM) and electric quadrupole moments of the W , ρ and K ∗ mesons with others computed in the literature for contributions from different nature. The gauge invariance requirement, along with the modification in the propagator inherent to the schemes, allows to identify the proper complex renormalization factor of the vector field, which keep the electric charge free of radiative correction contributions. II. FINITE WIDTH EFFECTS The schemes developed in [8–11] for the introduction of the finite width effects, while keeping electromagnetic gauge invariance, are based in two main observations: In quantum 2