Twitter and Instagram fell out last week over how photos from the latter are displayed on the former’s service. Now they’re competing more directly with their mobile apps too. Yesterday, Twitter added Instagram-style photo filters to its iPhone and Android apps through a deal with startup Aviary. Eight filters can now be used from within the app, with additional editing features to tweak images. Its launch came a couple of hours after Instagram pushed out version 3.2 of its iPhone app, with a redesigned camera, an extra filter (‘Willow’), closer integration with Foursquare, and other design tweaks. Cue more online discussion of whether Twitter is now an ‘Instagram-killer’. And is it? That depends on whether the value of Instagram is as an app for putting pretty filters on photos, or as a standalone social network in its own right. Artists as well as regular users will be mulling this question.