There is no 'Recycle Bin' option in Gallery / File Manager on Galaxy phones which makes it very tough to recover lost photos / files. Please, give this feature Samsung!!!
For Further assistance, you can get in touch with us via Live Chat option by following- http://livechat.support.samsung.com/Customer_new/IN. You can also connect us via Samsung Members web community by following mentioned url-https://community.samsungmembers.com/en_IN#/
If it was accidentally lost, I guess you didn't back up these photos in advance.First,check if your photos is still on your phone. This step MobiKin Doctor for Android free version can help you complete.If it is still there, then the Android recovery tool can help you recover. If not, there may be no way to recover.