Hi Bill,
Firstly I must point out I don't use either of the programs you mention, so I can only say what my process is. As long as the image doesn't require any 'artistic' adjustments such as can be applied using Photoshop or similar programs (for example the removal of people or litter etc) then I would import the image onto the timeline as it is. I usually put still images onto a separate track on the timeline to make it easier to spot them amongst the video clips, but you could import them onto the video track if the transition between video and still image requires you to do so.
I use Sony Movie Studio 12, which is their basic editor, and within this I resize and position the image within the frame where I want it, if required, and let the editor handle it from there. I don't resize in Corel Photo Paint, and certainly
never resize down to whatever resolution I think the final rendered output will be because this can add another stage of 'lossy' compression to the image, resulting in image degradation.
Obviously, if you are editing Full HD clips on the timeline but rendering to standard definition DVD then you are going to see a reduction in quality. Also, your 'preview' window on the editor might not reflect the exact resolution of your final output and may show a degraded image. In MS12 I can view at full resolution at full screen if I want to, and I do this on occasion if I am concerned about quality issues.
So my advice would be not to fiddle about with the images at all and import them straight from Flickr onto your timeline, reposition them if required, and leave it at that. Importing an image at its (higher) native resolution will also enable you to 'zoom in' or crop the image so that only a section of it is visible, useful if you want to inject a subtle movement into the still, without any noticeable quality drop.
Hope this helps
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