I believe you should be able to post to Lemmy from the Pixelfed instance, rather than just posting a link to the post. E.g., from Pixelfed, I believe you can just do something like post to @chat@lemmy.one and it will magically show up here, as being posted by your Pixelfed account.
But failing that, you can just use imgur or whatever other host you trust to host images.
In a perfect world, I think we'd all have access to something like IPFS and the image wouldn't have to live in one particular place.