I have heard that pornography is forbidden, but the reasons (most?) seem to be based upon statements in the Talmud that deal with situations where the potential for a sinful encounter may occur, from where is it known that even images are forbidden?
Wouldn't pornography by definition be "Ervah" prohibition? Deuteronomy 23, 15
כִּי֩ יְהֹוָ֨ה אֱלֹהֶ֜יךָ מִתְהַלֵּ֣ךְ | בְּקֶ֣רֶב מַֽחֲנֶ֗ךָ לְהַצִּֽילְךָ֙ וְלָתֵ֤ת אֹֽיְבֶ֨יךָ֙ לְפָנֶ֔יךָ וְהָיָ֥ה מַֽחֲנֶ֖יךָ קָד֑וֹשׁ וְלֹֽא-יִרְאֶ֤ה בְךָ֙ עֶרְוַ֣ת דָּבָ֔ר וְשָׁ֖ב מֵאַֽחֲרֶֽיךָ:
For the LORD thy God walketh in the midst of thy camp, to deliver thee, and to give up thine enemies before thee; therefore shall thy camp be holy; that He see no unseemly thing in thee, and turn away from thee.