Its difficult to tell, but I do have some forgeries which I found many years ago!
http://stampforgeries.com/forged-stamps-of-israel/ leads you top some pictures and Yacov Tsachor who is one of the experts who certifies this material and several references
. 3m of the First Definitive Issue, 1948. Altered perforations: Yacov Tsachor, "Holy Land and Israel Fakes and Forgeries – Examples from 1860-1948", Fakes Forgeries Experts journal, No.11 (August 2008): 39-48. Yacov Tsachor, "1948 Israel's First Coins – 3 Mils Perforated 10×10 Fakes", Fakes Forgeries Experts journal, No.9 (May 2006): 138-40.
2. 5m of the First Definitive Issue, 1948. Altered perforations: Yacov Tsachor, "Holy Land and Israel Fakes and Forgeries – Examples from 1860-1948", Fakes Forgeries Experts journal, No.11 (August 2008): 39-48.
7-9. 250m, 500m, and 1,000m of the First Definitive Issue, 1948. Leon Walters, "Philately of the Holy Land", Linn's Weekly Stamp News (August 23, 1965): 20,21. S.E. Hands, "The Interim Provisional Issues of Israel", The London Philatelist, Vol. 68 (March 1959): 46-52. Forgeries and fraudulent postmarks: S.N. Shure, E. Tolkowsky, J.M. Lees, G. Ward, H.H. Hirst, "The Postal Markings of Jerusalem Under the British Administration", The S.P.A. Journal, Vol. 19 (April 1957): 352-57. Anon. Note, The Holyland Philatelist, Vol. 3 (May-June 1957): 708,09. Anon., "Comparison of Genuine and Counterfeit Israel Nos.7-9" (from Minkus Publications, Inc.), Weekly Philatelic Gossip, Vol. 64 (March 5, 1957): 13,14. M. Hesky "News Letter from Israel", Stamp Magazine (U.K.), Vol. 16 (March 1950): 347. Norman Orenstein, "Everything Isn't Kosher In Israel", Weekly Philatelic Gossip, Vol. 56 (August 15, 1953): 764,66.