My apologies for no pictures, especially considering the content. I will try to get some uploaded soon to show a couple of good examples.
Let's say you have a chart and you show it in SharePoint using an Excel Web Access web part. Depending on the chart, it may show up looking the same as what it does in Excel. If so, have a nice day and read no further.
If (and this is quite common) it looks nothing like it, there is almost embarrassingly simple way to solve this problem.
Step 1: Use an Image web part instead (after all, it is an image right?)
Step 2: Use a jpg file. (Use my Chart Tools to export it)
And you're done. If you need extra help, leave a comment.