POST to specific resource

Hey,

I am thinking about allowing a POST to /images/12345 with content type for images, to upload a file. The meta info (size, etc.) has been send beforehand to /images thus creating /images/12345.

Is this spec compliant or a problem? I know I could do a PATCH to /images/12345 but uploading something should only be possible once. A PATCH would seem to imply the user can reupload an image to overwrite the other.

Hope you can help, thanks.