Yahoo has acquired GhostBird Software as part of its efforts to improve mobile access to its revamped Flickr photo-sharing service, and is reportedly considering multi-million dollar offers for two other app makers.

GhostBird is behind KitCam and the PhotoForge series, advanced photography apps for iOS. According to TechCrunch, KitCam allows mobile photographers to shoot with different “lenses” and “films”, and to manually adjust settings like white balance and exposure. No price was disclosed for the deal.

AllThingsDigital sources also suggest that Yahoo is considering a $50 million bid for automated video app maker Qwiki and has offered between $30 million and $40 million for Xobni, a maker of address book apps and plugins.

Qwiki makes an iPhone app that allows users to automatically turn photos, music and video into short movies with sources saying that Yahoo is in advanced talked to buy the company.

The GhostBird acquisition is the latest in a series of app acquisitions undertaken by Yahoo under CEO Marissa Mayer, the most audacious being the $1.1 billion it stumped up last month for the Tumblr blogging service.

Recent mobile app purchases include Stamped, a mobile recommendations app, and the Summly news reading app that it acquired in March for a reported $30 million. In April, Yahoo launched a new version of its iPhone news app using Summly.