Create an upload slot for a reference image. Returns an upload URL and a ref_ token: upload the image file with one shell command (curl -T <file> '<uploadURL>'), then pass the ref_ token to the reference-image parameter you are filling - every parameter that takes reference images names this tool in its description. This is the ONLY way to supply reference images, and those parameters accept ref_ tokens and nothing else. Image data never goes inside a tool call: a call is JSON, so an embedded image would have to be base64 text that you, the caller, must emit character by character - slow, error-prone, and enough to exhaust your context window. The upload moves the bytes out-of-band instead: a plain HTTP PUT of the raw file, so any HTTP client works; if your environment has no way to send one, install curl. And when the image you want is from one of your OWN recent Logospell generations, skip the upload entirely: pass sourceGeneration and sourceImage and the server copies it directly (to grow an existing set, use its extend tool instead: extend_image_set, extend_character_set or extend_illustration_set). Accepts PNG, JPEG, or WebP, each at most 500KB, each side between 64px and 768px - resize before uploading if needed; larger reference images do not improve results. A reference is private to your API key and can be used in any number of later calls; it expires 7 days after its last use or re-upload (each use restarts the window), so uploading a few references once can serve a whole session of work. To update a reference, upload a new file to the same upload URL: its image is replaced and its ref_ token stays the same. Costs no credits.