Yohan raises an important point to be considered: copyright. You will find an excellent treatise on copyright law, its purposes, general limitations and exceptions at http://www.unc.edu/~unclng/public-d.htm.
I am a retired attorney, cognizant of copyright law but not having an expert knowledge in it. I have taken a practical view of this issue, with due regard to the general law and its purposes. Firstly, this blog is not for profit but for educational and spiritual edification. None of my use of the art resources, whatever their source, have been for personal gain, and, if anything, have given that art exposure which may lead to greater personal gain to anyone who, perchance, has a copyright. Secondly, I have predominantly used art works that are older than a century and appear to be in the public domain. Those Twentieth Century works that I have used generally are from sites (such as http://www.biblical-art.com/biblicalsubject1.asp, particularly, and also http://www.artbible.info/ and http://www.spaightwoodgalleries.com/index.html) that appear to have made a serious and active effort to inquire into and protect any unknown copyright.
Yohan, as to your church’s use of any artistic expression on a church letter, it might be argued that the church is a non-profit organization and exempt, although that has serious problems and risks. It would be better to attempt to contact the source of the art to determine the copyright status and, if there are current copyright protections, to seek permission or waiver.
You will see in one of the early posts on this blog that I used art of my sister as a contemporary expression of the creation process and our response to it. She used an artistic style associated with certain artists and art pieces to express her own original response to the biblical creation stories. That is permissible under copyright law.
For a purpose such as you mention, I think you would be likely to obtain the most satisfying results by looking within your church body for talent and for contribution. Most churches have artistic talent within their folds that is not only competent but also invested in the church’s values, traditions and the life of its fellowship and, are willing to make a meaningful contribution to its body. My sense is that it is no different with your church. My suggestion is that you address your particular need to your larger membership. It enriches the fellowship, and pr0vides an opportunity for an individual or number of individuals to respond to the invitation or perceived need of the body for their own edification and that of the church. Never underestimate “God’s” gifts and work right there at home. And, when genuinely rendered, it involves no risk of copyright infringement.
Links to my site:
Home Page https://bibleartists.wordpress.com/