Remember that not all the icons represent value, especially if it's an icon of the 20th century. Icons of the Soviet era will be of value after some time. But one rule for determining the value of the icon works no doubt - the older you are, the more value it represents.
Consider the icon - if it depicts a special religious event, and even the author is a well-known painter, the value also increases. Talent fulfillment icons, originality, manners play an important role. Icons are very much appreciated by the schools of letters (e.g., Stroganov letter is quite rare). The plot may be non-standard and with little pictures on the edges (with the marks).
Great importance has artistic quality denomination – official Orthodoxy or the old believers. Especially if the icon is painted by hand, not industrially - she always has a substantial monetary value.
Ask for help from professionals. Experienced antique dealers to determine the age of the icons on the Board from the back side, but not everyone is able to do it accurately. Most often, the appraisal comes in color, quality of drawing, composition, freshness of ideas. If possible, consult with several specialists and antique dealers. Better if these people will be Museum professionals with huge experience.
Do not attempt to determine the value of the icons on the photos, because full information on its price is impossible to say. But don't ask for rating to little-known you and your friends or colleagues people. You can cheat, and for a pittance you sell a valuable rarity. Don't give an icon for restoration in the little-known centres of expertise - you just may not get your thing back to original condition.