That worked!

I changed my picture field from:

{INCLUDEPICTURE "{FILENAME \p}/../signatures/{MERGEFIELD "LastName"}.png" \* MERGEFORMAT}
to:


{INCLUDEPICTURE "{IF TRUE "{FILENAME \p}/../signatures/{MERGEFIELD "LastName"}.png"}" \* MERGEFORMAT}

and the pictures updated without the need to refresh the fields.

Thanks!