I've had very limited experience with photo/graphics as I'm not a graphic designer, so Paint.net is (I suppose) easier to use than other products.
I had 1 gif, 1 jpg, a canvas of 1050px x 150px
The gif was white, yellow and blue, the jpg was yellow filtered portrait.
I needed to make a web page banner, to make it easier to handle one object than 2 graphics, a background, and 2 text boxes.
I found it very difficult and frustrating- but I did it.
Paint.net doesn't constrain an imported graphic onto the canvas, but expands to hold the import. This is extremely annoying. Trying to drag handles on the graphic was frustrating and I gave that up and used a picture editor to resize it to 150px. I did this to both the graphic and the jpg. Now when I imported them, I could just place them, one on the far left, and one on the far right.
There was no option to flatten, but I could Merge Layer down!
Now I had to work out how to fill the space between the graphics!
So I drew a marquee (rectangle selection tool), used the sample tool (colour picker) and filled it with the bucket. If I didn't do that, then it wouldn't fill, or would cover everything up. You see, Paint.net seems to present the canvas with a white background and not transparent! More frustration.
The trouble with this is that I couldn't remove the focus from it. The only way was to save it, look at it with another program, re-edit it etc etc. More frustration.
The History didn't work as intended, so as I went backwards, it didn't reflect what was happening on the canvas.
Now somehow, (and I don't know how), I managed to remove the whitespace between the 2 graphics. If I did that, then I could fill without using a marquee.
When I Merged Layer down (I think), I could then go back and use the brush to remove the slight differences in colour between the jpg and the background.
Then I used 2 text boxes to add text, then merged the layer down.
I then saved it as a gif.
That's about it.
The banner isn't up yet, and I'll try and upload the finished banner so you can see.
OK There it is!
To see what I was up against, check the link in my first post. But it won't be there for too long.
Also check that I 'rubbed out' the left side of the pic so it would blend in with the background. Not perfect, but good enough.
I'm really very happy about the file size! That's one plus!