I want to attach some flag patches to my backpack but I don't want to sew or embroider them to the backpack. I saw some video about image transferred to fabric using techniques like mod podge transfer and I really like it. However, I realize this won't work for the patches that have white color background because I can't print white color to paper. Does any one know a better technique that will work with image that has white background color?
I'm not an expert on this technique, but this Instructables may be of help:
Here is the section on making transfers for dark fabrics that seems to overcome your problem of not being able to use white in your image:
Iron on Transfer Sheets for Dark Fabrics "If your shirt or fabric is black, dark gray, dark blue, or another dark color, you'll want to buy iron on transfer sheets for dark fabrics. They are thicker and have a white backing, allowing the use of white and light colors in the image or design. The major downfall of this type of transfer paper is that with the background appearing white, you cannot have part of your image appear clear... so you must carefully cut around any letters or other design elements or have a solid background as part of your design."
Additionally, here is a YouTube video showing the technique for tranferring onto dark fabrics, with links for buying the paper.
(note: Epson also makes and sells transfer paper for dark fabrics.)
https://www.youtube.com/watch?v=Xi_2X8sKifY "In this tutorial we cover the ways to use and the applications which transfer paper for dark fabrics."
One way to achieve a white background would be to transfer the image on to a white piece of fabric, trim around the image, and then attach that white fabric to your backpack. Depending on the fabric you choose, you may need to hem or seal the edges from unraveling. If you do not want to sew at all, you can buy "fray check" products to apply around the edges. Or if it is a plastic-based backpack you could even (very carefully!) melt the edge. (This might leave it too stiff or brittle, so best to practice on a scrap first.)
Since you mention not wanting to sew or iron on the backpack itself, another option is fabric glue! There are many formulas on the market, I would recommend looking for one marketed towards fabric or vinyl depending on the material of your backpack. (I haven't worked with backpacks like this so I won't recommend any here.)