Online appraisals are a great way to satisfy your curiosity about a particular item. The Wall Street Journal has investigated several of the online sites for accuracy. You can find the article online. If you need an appraisal for legal reasons such as estate documentation for a will or the IRS, for property division in a divorce, or for insurance reasons (a rider or a loss) you may need to have your antiques appraised by a qualified appraiser.
If you suspect that your antique is quite valuable you need a qualified appraiser. You can find on by checking out one of the three appraisal associations and locating an appraiser in your area with expertise on your particular item.
If you think that your item is not very valuable, go to an online resource for information. A qualified appraiser won't bother with things of little value.
Keep in mind that an online appraiser has only a photograph to look at. A physical examination can reveal aspects that a photograph can not.