Library Eusebius of Caesarea Life of Constantine
Book 4, Chapter 16: He forbids by Law the Placing his Likeness in Idol Temples.
In this manner he represented himself, even through the medium of painting, as habitually engaged in prayer to God. At the same time he forbade, by an express enactment, the setting up of any resemblance of himself in any idol temple, that not even the mere lineaments of his person might receive contamination from the error of forbidden superstition.
English translation by Ernest Cushing Richardson, in Nicene and Post-Nicene Fathers, Series II, Vol. I (eds. Philip Schaff and Henry Wace; Buffalo: Christian Literature Publishing Co., 1890). Public domain. Digital text via New Advent Church Fathers.