Jean,

Welcome!

There are two parts to the answer.

First, your gauge. You can determine the size you'll need for your image by making a gauge swatch. This is unique to you; your fiber, hook size and your own personal tension will be different from anyone else's. By figuring out the size you'll need and the number of stitches you'll need, you'll have the correct numbers you'll need for the image.

Second, you need to be working from an image that's the same size as what you want your finished item to be in stitches. So, for instance, if you wanted a 100x100 graph, you'd want to sort of get your image to 100x100 pixels. I say "sort of" because the software chooses the length for you, so you'd have to make an approximation. Since crochet stitches are rectangular, not square, you'd just have to kind of figure it by image proportion, not by actual number of rows for the length. (This will be addressed in a later version, but for right now, you can't designate the number of rows.)

Anyway, let's say it works out to 100x100 pixels. You'd reduce your image to 100x100 pixels. Unfortunately, you can't let the freePatternWizard do that for you, since it's not a graphics program. If you were to upload the large image to the freePatternWizard, you'd find it's going to skip over areas and won't produce an optimal result, and if your image is quite large, it will be a terrible result.