In this talk we are going to present how the Danish Agency for Data Supply and Efficiency (SDFE) transitioned from a purely proprietary system to an open source system based on SpatioTemporal Asset Catalog (STAC) API and Cloud Optimized GeoTiffs (COGs) for servingservicing its open data collection of 5 million oblique aerial images. The new system is built partly using existing open source components and partly on newly built open source components. It uses significantly less resources and lets third party users access the data in a standardized way. An important part of the process has been to develop and propose a community STAC extension for perspective imagery. This extends the STAC base metadata with parameters which are needed to do photogrammetric calculations and measurements using the images. The potential of this extension is that it enables the community to build generic perspective imagery clients in which the user can do advanced photogrammetric measurements. To ensure support for existing clients and to lower the barrier to entry the system also supports clients without COG reading abilities. Using open source components we have built "CogTiler" a high performance tile server which serves jpeg tiles directly from the COGs. Most of the time this is accomplished without decompressing the jpeg data. SDFE required that all code written for this project be open source and easily available to anyone. Therefore, all the code is available on GitHub.