According to the Terms of service of the official website of the Ministry of Foreign Affairs of the Republic of Bulgaria:

The content of the website of the Ministry of Foreign Affairs of the Republic of Bulgaria may be used freely unless explicitly stated that it is protected by the acting Copyright and Neighbouring Rights Act. Hence the use of text, photos, video and other visual elements published on the website is public domain and requires only mentioning the source.

It is therefore assumed that this photo, video or other image has been released into the public domain. However, in some instances the use of this image might be regulated by other laws.