I ask your permission to join this discussion even though I am not a Christian, I am a Jew. I want to help as many people as I can, whatever their faith, to overcome this problem of blasphemous thoughts. I suffered from them much of my life, and now have found much peace, thank the Lord. Please excuse me if I may be repeating some ideas already brought up by other participants.
These blasphemous thoughts are very disturbing to those of us who are religious because we view them as though they are real, and as something we created, and they are insulting to G-d. Yet we can approach or view the evil in our thoughts as no different from the evil we see outside of ourselves in the world. There is no denying there is evil, filth, and sin in the world around us, but it does not make us sinful, unless we chose to accept it. As religious, and G-d fearing people when we see evil and the potential for sin, we turn away from it and decide not to accept it, and we reject it as best we can. We don’t identify with the evil out there; we don’t see it as part of ourselves. We can take the same approach toward our internal world, in our minds. Unwanted, horrible thoughts can intrude into our minds, set off perhaps by certain conditioned cues, whether we think they are coming from our unconscious mind, our evil inclination, or from Satan. The key is we don’t have to believe or accept them. We need only acknowledge their falsehood, reject them and not identify with them.
I find it helpful now to distinguish between thinking something and believing it. What I noticed within me, with my OCD tendencies and my sometimes confused state of mind, was that thinking something was often confused with believing it was real. I learned that the important thing is what I do with a blasphemous thought. If such a thought intrudes into my awareness, I can see it for what it is - an evil, filth, a distortion, etc.., the same as when I might see something evil with my eyes that is out there, in the external world around me. I see it and may say that’s terrible, but I don’t accept it. When seeing something out there that I consider bad I certainly don’t dwell on it and focus my attention on it. No, I see it for what it is and reject it and move on. It is the same if we see something in our minds with our internal eyes. If we see an image or have a thought, it does not mean we have to believe it or accept it. We recognize that it is false. For example, I may have an image of G-d come to my mind which is very base. I make the clear distinction, and say no that’s not G-d, and may call it or say that it is whatever that image may appear to be instead of G-d, maybe a human image, maybe Satan, maybe even myself. We know that G-d is absolute perfection, absolute purity and absolute good, and if any of our distorted thoughts presents Him in any other way we can immediately realize that it is an absolute falsehood and need not believe or accept it. It helps to make a clear and absolute distinction, i.e., this thought is evil and the opposite of the truth, and is certainly the complete opposite of and has nothing to do with the Almighty. When a horrible thought comes to my mind I sometimes just silently say, “I declare that this a falsehood, I do not believe it, I will turn my attention now away from this evil and toward the true and only, absolutely pure and perfect Lord, and offer praise and prayer to Him.” I do not only declare it, I do it, I open my eyes and turn my head up, look up toward heaven and pray and praise Him. Turning away from our distorted thoughts or images, we can pray to the true and only G-d, and accept his infinite mercy and love.
I turn from the negativity of my thoughts to the joyful, positive praising of the Lord. Staying in a rejected negative, down or depressed feeling state only invites evil and sinful thoughts. So it is our obligation to not stay feeling dejected and down, but rather to turn to and praise G-d joyfully. Also, we know that G-d is not petty and vindictive. His compassion and love is not small and limited like that of humans, it is unlimited, boundless and infinite. He understands our minds and thoughts, better than we ourselves ever can, and looks into our hearts for what we truly believe and accept. He knows us, accepts us and loves us.
“When my anxious thoughts multiply within me, Your consolations delight my soul” (Psalm 94:19).
Wishing you and your family a happy 4th of July. May God bless 
