Denim can be different, so please test your own jeans before engraving. These were stretchy jeans and image shows what was in the fabric. Also, the engraving settings are very different for photo and vector images. It’s important to make sure the power is not too high and speed too slow, or the fabric will fall apart after engraving. 

Everything was done in XCS and all my settings are shown in photos. I started by removing the background around the dog’s face and edited grayscale a bit. You also must invert the image, because the fabric is dark. 
Also, the bigger the image, the better. It makes it look nicer on fabric and details show better. 

I used images from XCS library. Those images and text engrave beautifully and look perfect. My settings for this fabric are in photos. The first photo was set to ignore while engraving the second part of images (the name and snowflakes). 

The engraving usually takes seconds, and including the image editing time, you can have a unique piece of clothing in minutes!

Just a reminder to make sure your power is not too high or speed too slow. You want the engraving to just look lighter blue, and not have any yellowing on it. If it has yellow tint on the images, you’ve gone too far and the fabric will fall apart. 
Try different images on the pockets, or sides and bottoms of pant legs for your own unique design. 
Enjoy! :)