HTTP API to get the image of an nft based on contract and NFT ID?

If you get the "tokenUri" of the NFT and paste it to the browser

      ipfs://tokenUriHERE

You will see the NFT metadata in a json format like this.

{
   "name": "name it",
   "image": "ipfs://QmR36VFfo1hH2RAwVs4zVJ5btkopGip5cW7ydY4jUQBrKW",
   "description": "description",
   "attributes": [
        {
          "trait_type": "Artist",
          "value": "value"
        },
] }

If you get the image URL and paste it to the browser you will see the image.

If you want to write a code to fetch data, just send get request to ipfs://tokenUriHERE get the JSON, retrieve the image and then get the image.

Or you can use libraries. In javascript, web3.storage

import { Web3Storage } from 'web3.storage'

const token = process.env.API_TOKEN
const client = new Web3Storage({ token })

async function retrieveFiles () {
  const cid =
    'bafybeidd2gyhagleh47qeg77xqndy2qy3yzn4vkxmk775bg2t5lpuy7pcu'
  // You can fetch data using any CID, even from IPFS Nodes or Gateway URLs!
  const res = await client.get(cid)
  const files = await res.files()

  for (const file of files) {
    console.log(`${file.cid}: ${file.name} (${file.size} bytes)`)
  }
}

retrieveFiles()

If you're building with React, there's a great library use-nft from spectre.xyz that helps abstract away the inconsistent formatting of NFT metadata to give you the relevant URL for displaying the image.

You can install it with:

npm install --save use-nft ethers

Before using it, you will have to wrap your app in a provider as shown here but the actual usage is very easy.

function Nft() {
  const { loading, error, nft } = useNft(
    "0xd07dc4262bcdbf85190c01c996b4c06a461d2430", // NFT contract address
    "90473" // token ID
  )

  // nft.loading is true during load.
  if (loading) return <>Loading…</>

  // nft.error is an Error instance in case of error.
  if (error || !nft) return <>Error.</>

  // You can now display the NFT metadata.
  return (
    <section>
      <h1>{nft.name}</h1>
      <img src={nft.image} alt="" />
      <p>{nft.description}</p>
      <p>Owner: {nft.owner}</p>
      <p>Metadata URL: {nft.metadataUrl}</p>
    </section>
  )
}