There is nothing wrong with tracing it is merely copying and copying is copying, whether it is done by tracing or by eye. The latter is more impressive certainly, but it is the end result that counts, especially with digital art, so how you achieve your results is simply a matter of personal preference.

As for those on other forums who object to tracing, point out to them that some old masters used cameras, Vermeer for example was thought to have used a camera and Durer is famous for using a "tracing frame". Many big name illustrators of today have professional photographers take reference images for them to trace/copy.

Just one small note of caution, remember that most photos that you find on line will be copyrighted. You can trace them to your hearts content and even publish the results on line - as along a you neither; claim the original as your own, make money from them, use them to advertise a money making enterprise or use them in a way that will bring disrepute to the owner.

What this means is; if you are just doing this for fun, then for the most part you will get away with using any image in a reasonable manner (i.e. not as part of some sleazey gonzo-porn-pirate-international scamming site or some such). If the owner objects to your use of his image, then you may have to take it down, this is not always backed up by law, when the image is used for non-profit reasons, but most site operators will want to avoid any threat of lawsuits and will usually back such demands.

If you are meaning to go on to look for work using these images, you should ask the originator if you can use them. They will often agree if you include a credit or sometimes a link to their site. Many glamour models actually ask pro or even amateur illustrators to use their photos if you want to try pin up art at some time.

In any case, it's good practice to credit the originator/owner, where you can, even if you don't ask them for permission.