Thanks, @JonahLay!
Upon further digging, I have a follow-up question. I get a different Share as Web Layer pane for the same image depending on whether I select the option by right clicking on the layer in a map's table of contents or if I select the option by right clicking on the same file in the Catalog pane. Here are the results of both actions:
This is the result of right-clicking on a raster image in the TOC and selecting Sharing > Share as Web Layer:
And this is the result of right-clicking on the same layer in the Catalog Pane and selecting Share as Web Layer:
The latter results in successfully publishing the layer to Enterprise, while the former publishes a layer, but unsurprisingly it's not a raster layer and won't draw.
At first I thought this wasn't a big deal because I could just publish the image from the Catalog pane, but then I realized that's not a perfect solution because I might want to modify the layer in the map prior to publishing. For example, I want to publish my image with a transparent background, but I'm not able to make that change in the map and then publish it. Publishing the file from the Catalog pane results in a hosted image layer with a black background.
How can I publish my image with a transparent background from Pro if I can't publish from the TOC? Or is there something I can do differently so that I can successfully publish the image from the TOC?
Thanks again for all your help!
- Holly