When I place a photo in AI and then I want to separate 2 parts of an object-let's say, a shoe (it is a jpg image). I want to separate the upper part from the out sole. So, I do a path, then select, then Pathfinder -> Divide but then the whole picture moves and I don't manage to separate them properly! Maybe I am doing something wrong when I place the photo in AI and therefore it becomes "mobile"? I see the photo with the a blue anchor square around it. I guess that is the issue? How can I solve this?
You can't use pathfinder on raster images (e.g. JPG, PNG), it only works on paths – it's as simple as that.
If you want to separate parts of an image your best bet is to use clipping masks. Or use a raster image editor such as Photoshop (and import the parts in to Illustrator as distinct images of you need to).
To use clipping masks in Illustrator:
- Duplicate your image for as many distinct parts as you want.
- Draw a path over the part you want to mask.
- Select the image and your path and go to "Object → Clipping Mask → Make" or hit ctrl / cmd + 7.
- Repeat as desired.
You can read more about clipping masks in Illustrator here: