The Concise Oxford English Dictionary offers for this context the following definition of the word "modest":
(esp of woman) decorous in manner and conduct, scrupulously chasteMy edition dates back to 1982, so the qualification "esp of woman" might have been removed from more recent editions. Modesty clearly applies just as much to men as it does to women.
The Catechism of the Catholic Church discusses modesty in the context of the Ninth Commandment and in reference to purity and chastity.
2521 ....Modesty protects the intimate center of the person. It means refusing to unveil what should remain hidden. It is ordered to chastity to whose sensitivity it bears witness. It guides how one looks at others and behaves toward them in conformity with the dignity of persons and their solidarity.
2522 Modesty protects the mystery of persons and their love. It encourages patience and moderation in loving relationships; it requires that the conditions for the definitive giving and commitment of man and woman to one another be fulfilled. Modesty is decency. It inspires one's choice of clothing. It keeps silence or reserve where there is evident risk of unhealthy curiosity. It is discreet.
2523 There is a modesty of the feelings as well as of the body. It protests, for example, against the voyeuristic explorations of the human body in certain advertisements, or against the solicitations of certain media that go too far in the exhibition of intimate things. Modesty inspires a way of life which makes it possible to resist the allurements of fashion and the pressures of prevailing ideologies.
2524 The forms taken by modesty vary from one culture to another. Everywhere, however, modesty exists as an intuition of the spiritual dignity proper to man. It is born with the awakening consciousness of being a subject. Teaching modesty to children and adolescents means awakening in them respect for the human person.
2525 Christian purity requires a purification of the social climate. It requires of the communications media that their presentations show concern for respect and restraint. Purity of heart brings freedom from widespread eroticism and avoids entertainment inclined to voyeurism and illusion.The BBC report linked above suggests that in at least one case the leaked photographs are not recent, and suggests that the celebrity involved may recognise in some way a certain regret about them, reportedly having deleted them herself a long time ago.
The media reporting, however, seems to focus exclusively on the "scandal" caused by a security breach that has revealed photographs from private electronic accounts. A privacy lawyer is quoted in The Times' coverage, for example, as saying:
... the leak was a "shocking" violation of privacy given its scale and content.The security breach and the violation of privacy seem to be more the cause of scandal than the content of the photographs themselves (but see Fr Alex' comment here).
Should not the question of modesty - in reference to both the taking of the original photographs and in reference to their publication - not also be part of the media conversation? Clearly the different photographs will have been taken in a range of different circumstances, and it would therefore be quite wrong to adopt an attitude of condemnation towards those the details of whose actions are not known to us. But at a time when the use of smart phones by young people to share "intimate photographs" of each other ("sexting") is a serious concern, does not this occurrence provide a salutary warning in favour of modesty? The question of what photographs it is - or is not - appropriate to take seems to me an important part of the public debate, and we might begin to expect celebrities to set a good example in this regard.
[Modesty is not just a question for those who hold religious beliefs. Its relation to the dignity of the person means that it is a notion accessible also to those who hold no religious belief.]