Welcome to Anvil’s Community Forum!
Let’s start here: Valid arguments and return values. Anvil knows how to convert some kinds of data objects, for transmission over the wire, but it can’t possibly know how to do every data type. This is especially true when the type is defined outside of Anvil.
Fortunately, an image is effectively a binary file. And Anvil gives you a way to package up binary files. See Files, Media and Binary Data. With this approach, you can handle images. The Media Object, received in the browser, can then be displayed directly in the UI via an Image or Link component