Many posts on Chemistry Stack Exchange benefit from figures, including molecular and crystal structures, graphs, instrumentation, experimental setups and experimental results. Sometimes, animations and short movie clips are also easier to understand than a verbal description.
Where do we find these figures or how can we make them?
A quick way to draw the structure of a molecule is to look up the SMILES description of the molecule on pubchem or another cheminformatics site. To give an example, the SMILES of caffeine is CN1C=NC2=C1C(=O)N(C(=O)N2C)C.
Then, you can load this into a chemistry drawing program such as Chemdraw (commercial) or MarvinJS (online demo) or PubChem Sketcher. If necessary, you can change the orientation, make small change (e.g. change $\ce{#CH}$ to $\ce{#C-H}$) and add other molecules. Then, you can output an image, either a Lewis structure (with or without "lone pairs") or a skeletal structure. Here are the MarvinJS images (choosing 400 by 400 pixel size):
For a crude way of sizing the image, you can append a "b" or "s" to the image name after it is loaded, making it smaller.
You can also get an entire reaction by using reaction SMILES such as
CC(=O)O.OCC>[H+]>CC(=O)OCC
rendering
JSmol is able to load common molecules using the cactus.nih server. For example, to get a quick 3D image of trans decalin, you load it, turn on zshading (set zshade on), save and upload the image.
With some more work, you can also screen capture the rotating image and turn it into an animated GIF.
If you need a standard textbook figure, one strategy is to use google image search, limiting the search to a domain. For example, the search term
libretexts.org:activation energy
will search for images concerned with activation energy on the libretexts sites. Here are the first couple of hits:
Many of these show the energy vs reaction progress diagram we are familiar with. Some also have a Maxwell Boltzmann distribution for different temperatures. You can filter for large images to get those of highest resolution, if this is important.
You can do a reverse image search using google. For example, I made this image. Someone might find a low-quality version such as this one.
Reverse-image search will yield several pages that include the image, some at much higher resolution.
