Where does Judaism say tattoos are prohibited?
Leviticus 19:28 is the verse used to teach that tattoos are forbidden. Since as early as the Mishna (around 400BCE) Jewish commentaries have tried to explain, interpret, understand the verse. Generally speaking, all modern denominations of Judaism still consider it a mitzvah (commandment) not to get a tattoo. However, the conversation is never over and different groups of Jews engage differently with the mitzvot.
Wow! Judaism has been struggling with this issue for a long time. Is that important?
Yes. It is significant that for centuries and centuries our scholars and philosophers and "wise people" have been trying to determine with the verse means, what a tattoo is, and the specific act being forbidden. This tells us that for all this time Jews have either been getting tattoos or have been tempted to get tattoos. (Otherwise, why would anyone care to talk about it?)
Can I be buried in a Jewish cemetery if I have a tattoo?
Yes! The myth that Jews with tattoos are not allowed to be buried in Jewish cemeteries is not based in any identifiable Jewish text or law. Getting a tattoo is considered to be a negative mitzvah (something we are prohibited to do) but transgressing a mitzvah does not preclude someone from being buried in a Jewish cemetery or in any Jewish manner.
But my mom said I can't be buried in a Jewish cemetery...
Your mom is misinformed. (I'm sure she's amazing and right about most things - this time, though, she's wrong.) Many people still believe this but it simply is not true. One of the greatest things we can do is to honor and care for someone who has passed away. This means preparing their body for burial and performing all the rituals around burial. This is so highly valued because it is a truly selfless act - the deceased can not "repay" us for our care. For this reason, no Jewish cemetery would ever refuse a Jew a proper burial (at least to my knowledge).
Is getting a tattoo worse than eating a cheeseburger?
No. Both are technically prohibited according to Jewish law. However, according to Jewish tradition, all of the mitzvot are considered equally important. We are commanded to act in certain ways, eat certain foods, wear certain clothes... There is no hierarchy of mitzvot. In the Reform Movement, we view mitzvot as guidelines for living and encourage people to engage with the text and tradition to determine how best to practice Judaism for themselves. For some this means keeping kosher, for others being conscious of where and how their food is sourced. For some the prohibition against tattooing is less important than the prohibition against withholding wages. There are many mitzvot in our tradition (613, actually) and Reform Judaism teaches us to work to make Judaism (as a whole) enriching, fulfilling, and meaningful in our lives. Sometimes means choosing not to follow a particular mitzvah but, perhaps, focus more on another one.