Generally, if the claimed deduction for an item or group of similar items of donated property is more than $5,000, you must get a qualified appraisal made by a qualified appraiser, and you must attach Section B of Form 8283 to your tax return. There are exceptions, discussed later. You should keep the appraiser's report with your written records.

For more information (including "exceptions"), please refer to this IRS Pub. 561 -
Determining the Value of Donated Property:

https://www.irs.gov/publications/p561/ar02.html#d0e1485