How do I write p permission letter to use someone's copyright?

Just ask. Contact the copyright holder in writing; many rightsholders have online forms to simplify the process.

Ask the copyright holder. Do it in writing, and be specific as to your planned usage.

In most cases yes, permission is required to use copyrighted material. There are exceptions however. The "fair use" exception allows for the use of a portion of a copyrighted work, without...

Make an agreement, generally in writing, which spells out exactly what you're allowing them to do.

ltc