Even if they are “obcene” or “anti-Christian” please do not worry yourself.
If you were Catholic at the time, and you haven’t already done so, take these to confession and then forgive yourself.
We have had several individuals come thru our RCIA class with tattoos and these are a part of your past. So just like my saint’s medals, these may very well help to serve you by reminding you from whence you came and where it is that you now desire to be in the eyes of God. Let no-one deride you about these, for God sees into your heart, past the flesh.
These tattoos may also serve as a means to help you spread the Gospel. Someone may feel more at ease around you when discussing your faith. They may even try to point out the errors of your past life via these tattoos, was not the Apostle Matthew a tax collector? Did not several of the other Apostles have a not so clean and sparkling past? So you have a means to show that anyone with the true desire can find the light and the path. You might even get that person to attend an RCIA class, because they feel “safe” due to this communality with you and the tattoos… God can work miracles thru you, just the way you are!
If you can cover these up at another time, and this what you feel called to do, then do so; however, in the meantime - please do not place undue stress upon yourself, nor allow others to do so. If they judge and condemn you, they do so to themselves as well.