Wrong answer. OP said " and still keep shadows such as a skirt casting a shadow on a characters leg?" Turning off cast shadows will not still keep shadows elsewhere - there will be no shadows at all. Lights should always cast shadows, otherwise things look like stupid Poser images.

Do not use the Diffuse_Color channel. Connect the image to Color if you're talking about the Background material.

If this is an ordinary prop being used as a background, connect the image to Alternate_Diffuse and set it to white. The Alternate_Diffuse channel is supposed to be where you plug in your own choice for lighting model. However, if you just plug an image straight into it, then there is no lighting model and the image will be self lit. Thus, it is not affected by lights, in which case it also is unaffected by shadows.

Set Diffuse_Color to black or Diffuse_Value to 0 to shut it off. Also set Specular_Value = 0.

---

Renderosity forum reply notifications are wonky. If I read a follow-up in a thread, but I don't myself reply, then notifications no longer happen AT ALL on that thread. So if I seem to be ignoring a question, that's why. (Updated September 23, 2019)