Is there a way to straighten out this curve in my butt crack? (Photo)

Allow me to answer your question as best i can based upon your limited view photo. However, please keep in mind that an in-person consultation with physical exam is first necessary before any legitimate evaluation or final surgical recommendations are made. It is possible that liposuction of the larger convex side of the curve may straighten it out some. Glad to help

It is very difficult to determine the exact size and shape implant you will require to best match your ideal butt image without an examination by a board certified plastic surgeon. Not just any board certified plastic surgeon, but one with many years of frequently performing breast augmentation surgery including different approaches, techniques and implant choices. This is because several measurements not to mention your breast characteristics are needed to determine the optimal implant size to obtain your goals. Without knowing these dimensions it would be difficult to make this determination. For example, the existing base width of your buttock will determine, in many cases, the maximal volume per implant profile that you can accommodate. Liposuction of your lower back and fat transfer is also helpful as an adjunct to implants. Using “want to be” photos however are useful if simply provided to the surgeon.

From what I can tell, I think this is just the way you were born with an extra cleft of this area.  If this really bothers you, lifting that area up and adding fat graft into the focused area is the approach I would try initially.  Best Wishes!!

Dear Sandyklein,you might consider fat transfer but it is hard to tell for sure without an examination. I would suggest you to consult a board-certified plastic surgeon. Only after a thorough examination you will get more information and recommendations.Daniel Barrett, MD, MHA, MS 
Certified, American Board of Plastic Surgery  
Member, Am. Society of Plastic Surgery

Hello dear!
Thanks for the picture and provided information as well.
Based on your photos, you are a good candidate for fat transfer, to fix your problem, and I think you'll get very good results. 
l recommend you to make an in-person consultation with a board certified plastic surgeon for a proper answer and to talk about your goals and anything you need to know.
Good luck :)

Yes, moderate lipotransfer, skillfully done could address your concern. This area is located in the lower part of your tail bone and your plastic surgeon has to be mindful about not damaging the critical anatomical land marks.

 The area you are referring to is often called the gluteal cleft. Midline structures in the body can often cause unique peculiarities because of embryological development. Often during early embryology midline structures have not get formed but I rather from the left and right sides coming together. The most common medical condition in the area you describe I called pilonidal cyst.  Be happy if you don't have those. There is a substantial amount of connective tissue holding the crease down to the underlying bony structures in the area will not release with fat transfer. If the area really bothers you it's possible to break up the single line with the procedure called a Z-plasty.  It would leave a zigzag scar.I don't think you would be interested in this.Better to leave good enough alone.Best,Mats Hagstrom M.D.