It is permissible for a woman with whom the marriage contract has been done to uncover part of her body or adornment to the one who did the marriage contract with her, because she is his wife, and Allah says (interpretation of the meaning):
“5. And those who guard their chastity (i.e. private parts, from illegal sexual acts)
6. Except from their wives or (the slaves) that their right hands possess, __ for then, they are free from blame;
7. But whoever seeks beyond that, then those are the transgressors”
There is nothing wrong with that being done via the internet, so long as the conversations or pictures are not preserved, and so long as precautions are taken to ensure that no one has access to them or is spying on them.
But we do not advise anyone to do that, because it may result in someone else seeing those images and because it may lead to extreme provocation of desire for either party at a time when there is no legitimate way of fulfilling it; this may push them towards masturbation which is forbidden in sharee‘ah.
And Allah knows best.