In the sentence
In questa fotografia ci sono delle piccole case in legno
you are saying that you see a bunch of small wooden houses, more than two but relatively few. The form 'delle piccole case' is the plural of 'una piccola casa', the partitive article delle acts as the plural of indefinite article una and can easily be replaced with 'alcune', i.e. 'some' in English.
If you say
In questa fotografia ci sono piccole case in legno
without any particular emphasis, most people would understand that there are at least two small wooden houses, without making specific assumptions whether these are few or many; as per egreg's comment, this might be enough. However, as pointed out by Bakuriu, depending on intonation, pauses, context, etc., people might even think that small wooden houses is all that you can really see in the picture.
The same applies to your other example.
My point of view is that the use of partitive articles depends on whether you intend to specify the relative scarcity of something or not. For example, in poetry, partitive articles can be omitted to create a sense of indefiniteness, vagueness:
Navi vanno laggiù e cercano nel vento il nuovo orientamento della rotta alle Indie
Are all ships going there? Only few of them? More and more everyday? After all, the fact that ships are going there is more important than their number: they are changing the world alright.