There is also a transparent pet archive here for pets you don't own;
https://cstranspets.weebly.com/And for ones you own, if you don't have any image editing software, you can also get a transparent image by using the
scenes feature, just open any scene and navigate to the pet like you are going to add it onto the scene, if you right click the pet and grab the image URL/image link from there, it'll be transparent when posted.